A Phase 4 Study to Evaluate the Efficacy, Safety, and Tolerability of Mirabegron in Male Subjects With Overactive Bladder (OAB) Symptoms, While Taking the Alpha Blocker for Benign Prostatic Hypertrophy (BPH)

Inclusion Criteria: at Visit 1 (Screening): * Patient had been under treatment with tamsulosin 0.2mg for at least 4 weeks before the start of the Screening period. * Patient with a history of an average of at least 2 episodes of urgency per 24 hours and an average of 8 or more micturitions per 24 hours during the last 3 days before the start of the Screening period (verified by interview). * Patient who had no wish to have children in the future (Unique to Japan). * Male subjects and their female spouses/partners who were of childbearing potential must be using highly effective contraception consisting of two forms of birth control (at least one of which must be a barrier method), starting at Screening, continuing throughout the study period, and for 28 days after the final study drug administration. * Subject must not donate sperm, starting at Screening, continuing throughout the study period, and for 28 days after the final study drug administration. * Patient was willing and able to complete the micturition diary and questionnaires correctly. * Subject agreed not to participate in another interventional study while receiving treatment in this study. at Visit 2 (Baseline): * Subject with an average of at least 2 episodes of urgency per 24 hours and an average of 8 or more micturitions per 24 hours based on a 3-day micturition diary from the Screening period. Exclusion Criteria: at Visit 1 (Screening): * Patient with suspected symptoms of OAB, with onset only transient (e.g., drug-induced, psychogenic). * Patient with PVR urine volume \>100 mL or Q max \<5 mL/sec. * Patient with prostate-specific antigen (PSA) ≥4 ng/mL. * Patient with neurogenic bladder (e.g., spinal-cord lesions or other damage that will clearly affect urination; multiple sclerosis; Parkinson's disease) or a history of surgery that caused damage to the pelvic plexus. * Patient with urethral stricture or bladder-neck stenosis. * Patient with diabetic neuropathy complications. * Patient who had undergone a surgical procedure, previous pelvic radiation therapy, or hyperthermia therapy that may affect urinary tract function. * Patient with significant stress incontinence or postsurgical prostate incontinence, as determined by the Investigator. * Patient with an indwelling catheter or practices intermittent self-catheterization. * Patient with 3 or more episodes of recurrent urinary tract infection (UTI) within the last 6 months. * Patient with a UTI; prostatitis; chronic inflammation, such as interstitial cystitis; urinary calculus; or previous or current malignant disease of the pelvic organs. * Patient with a concurrent malignancy or history of any malignancy (within the past 5 years), except for non-metastatic basal-cell or squamous-cell carcinoma of the skin that had been treated successfully. * Patient with serious heart disease, liver disease, kidney disease, immunological disease, lung disease. * Patient who had received intravesical injection within the last 12 months with botulinum toxin, resiniferatoxin, or capsaicin. * Patient who had received electrostimulation therapy for OAB. * Patient who had received a bladder training program or pelvic floor exercises \<28 days prior to the start of the Screening period. * Patient with postural hypotension or syncope, hypokalemia, or closed-angle glaucoma. * Patient with evidence of QT prolongation on electrocardiogram (ECG), defined as QTcF \>450 msec. * Patient with severe uncontrolled hypertension, defined as sitting systolic blood pressure (SBP) \>180 mmHg and/or diastolic blood pressure (DBP) \>110 mmHg. * Patient with a clinically significant ECG abnormality, as determined by the Investigator. * Patient who had severe renal impairment, defined as an estimated glomerular filtration rate of \<29 mL/min/1.73m2; end-stage renal disease; or is undergoing dialysis. * Patient with aspartate transaminase (AST) or alanine transaminase (ALT) \>2 times the upper limit of normal (ULN), or gamma-glutamyl transferase (γ-GT) \>3 times the ULN and considered clinically significant by the Investigator. * Patient with moderate or severe hepatic impairment, defined as Child-Pugh Class B or C. * Patient with hypersensitivity to any of the components of mirabegron, other beta-adrenergic receptor (β-AR) agonists, or any of the inactive ingredients. * Patient with ongoing alcohol and/or drug abuse. * Patient with or a history of mood disorder, neurotic disorder, or schizophrenia. * Patient with dementia, cognitive dysfunction, or clinically significant cerebrovascular disorder. * Patient who had been treated with an experimental device \<84 days or received an investigational agent \<84 days prior to the start of the Screening period. * Patient had used any prohibited concomitant medication \<28 days (but, \<1 year for 5α-reductase inhibitors) before the start of the Screening period. * Patient with any clinically significant condition, which in the opinion of the Investigator, made the subject unsuitable for study participation. * Patient who was involved in the conduct of the study as an employee of the Astellas group, a third party associated with the study, or the study site team. at Visit 2 (Baseline): * Subject fulfills any exclusion criteria of Visit 1 at Visit 2. * Subject was noncompliant during the 4 week tamsulosin Screening period, defined as taking less than 80% or greater than 120% of prescribed dose of study medication. * Subject had an average total daily urine volume \>3000 mL, as recorded in the 3-day micturition diary.