A Study of ASP1941 in Combination With Insulin in Patients With Type 1 Diabetes Mellitus

Inclusion Criteria: * The subject has been diagnosed with type 1 diabetes mellitus * The subject has been receiving insulin therapy for the treatment of diabetes mellitus. * The subject has not switched from an insulin product to another insulin product or switched between continuous subcutaneous insulin infusion (CSII) and multiple daily injections (MDI). * The subject has an HbA1c value between 7.5% and 11.0% and the difference of HbA1c value is within ± 2.0%. * The subject has a fasting blood C-peptide level \< 0.6 ng/mL. * The subject has a body mass index (BMI) between 20.0 kg/m2 and 35.0 kg/m2. Exclusion Criteria: * The subject has type 2 diabetes mellitus. * The subject has participated in a clinical study or post marketing study of another drug or medical equipment within 12 weeks (84 days) before providing written informed consent, or is currently participating in such a study. * The subject has received treatment with ASP1941 (ipragliflozin) or participated in a clinical study of ASP1941 (excluding subjects who discontinued before the investigational period). * The subject participated in this study previously. * The subject has received a hypoglycemic agent other than insulin or an α-glucosidase inhibitor. * The subject has proliferative retinopathy (except for those who have undergone photocoagulation etc. and whose symptoms are stable). * The subject has experienced severe hypoglycemia. * The subject has experienced diabetic ketoacidosis. * The subject has chronic disease that requires the continuous use of corticosteroids, immunosuppressants, etc. * The subject has symptomatic urinary tract infection or symptomatic genital infection. * The subject has a history of recurrent urinary tract infection or recurrent genital infection. * The subject has a history of cerebral vascular attack, unstable angina, myocardial infarction, vascular intervention, or another serious heart disease. * The subject has a concomitant malignant tumor or a history of malignant tumor * The subject has a history of an allergy to ASP1941 (ipragliflozin) and/or similar drugs (drugs possessing SGLT2 inhibitory action). * The subject has psychiatric disorder that is inappropriate for participation in the study. * The subject has drug addiction or alcohol abuse. * The subject has severe infection or serious trauma, or is perioperative. * The subject has a history of medically significant renal disease such as renovascular occlusive disease, nephrectomy and/or renal transplant. * The subject has any symptoms of dysuria, anuria, oliguria, or urinary retention. * The subject has severe renal impairment or end-stage renal failure requiring dialysis. * The subject has an Aspartate Aminotransferase and/or Alanine Aminotransferase value that exceeds 2 times, or a total bilirubin value that exceeds 1.5 times the upper limit of the reference range. * The subject has uncontrolled severe hypertension. * The subject has serious gastrointestinal disease or a history of operation for serious gastrointestinal disease.