Study of a α1A Adrenoceptor Selective Antagonist Silodosin to Treat Severe Benign Prostatic Hyperplasia(BPH)

Inclusion Criteria: * Is at least 50 years old * Has a urinary disturbance associated with severe BPH and has a total IPSS score 20 or higher * Has a QoL score of 3 or higher * Has a urine volume of 120mL or greater and a Qmax of below 15mL/sec * Has a PRV of below 100mL * Voluntarily decides to participate in this trial and sign with informed consent form Exclusion Criteria: * Has been administered silodosin * Has been administered an α1A-adrenoceptor blocker within one month * Has been prescribed antiandrogens except 5α-reductase inhibitors within a year * Has had phytotherapy within 3 months * Has had prostatectomy * Has had intrapelvic radiation therapy * Has had transurethral microwave hyperthermia of transurethral needle ablation * Is suspected to have implications that are likely to affect urine passing such as neurogenic bladder, bladder calculus or active urinary tract infection (UTI). * Is conducting self-catherterization * Has a renal impairment with a serum creatinine of 2.0mg/dL or greater * Has severe hepatic disorders (hepatic insufficiency, cirrhosis, jaundice, hepatoma) or has a total bilirubin of 2.5mg/dl or higher or has AST/ALT 2.5 times higher than the normal (upper) level * Has suffered from a severe arrhythmia, cardiac failure, cardiac infarction, unstable angina, cerebral infarction within 6 months * Has experienced allergy to α1 receptor blockers * Has orthostatic hypotension around the time of Screening Visit * Has participated in other clinical trials within 8 weeks prior to Screening Visit * Has a Prostate specific antigen(PSA) of higher 10ng/mL or has been diagnosed with tumor identified by a biopsy even though he has a PSA of lower 10ng/mL (Patient who has been administered 5α-reductase inhibitors for more than 3 months are presumed to have 2 times higher than their actual PSA levels) * Has been taking unstable dosing of 5α-reductase inhibitors like finasteride or dutasteride for the past 3 months or is expected to change the dosage during the trial.