A Study to Assess the Efficacy and Safety of ASP1941 in Combination With Metformin in Asian Diabetes Patients

Inclusion Criteria: * Diagnosed as type 2 diabetes mellitus patient at least 12 weeks before the study * Stable diet and exercise program for at least 8 weeks before the study * On a stable dose of at least 1500 mg/day metformin monotherapy or at least 1000 mg/day metformin monotherapy for the subject who can not titrate up to 1500 mg/day due to safety concern of metformin * BMI of 20.0 to 45.0 kg/m2 * A HbA1c value between 7.0 and 10.0% at screening AND does not meet any of discontinuation criteria on fasting plasma glucose Exclusion Criteria: * Type 1 diabetes mellitus * Proliferative diabetic retinopathy * Receiving insulin within 12 weeks prior to the study * History of clinically significant renal disease(s) * Significant dysuria caused by a neurogenic bladder or a benign prostate hypertrophy etc. * Urinary tract infection or genital infection * Continuous use of systemic corticosteroids, immunosuppressants, or loop diuretics * History of cerebrovascular attack, unstable angina, myocardial infarction, angioplasty, serious cardiac diseases within 12 weeks prior to the study * Severe infection, serious trauma, or perioperative subject * Known or suspected hypersensitivity to ASP1941 * History of treatment with ASP1941 * Participated in another clinical study, postmarketing study or medical device study within 12 weeks before the study * Serum creatinine value exceeding the upper limit of normal range * Urinary microalbumin/urinary creatinine ratio \>300 mg/g