A Study to Evaluate Long-term Safety and Efficacy of ASP1941 in Diabetes Patients

Inclusion Criteria: * Type 2 diabetes mellitus patients * Subject is only on a diet and exercise program or has received a single antihyperglycemic agent or two antihyperglycemic agents (excluding insulin) with low dose (≤50% of the maximum dose of each recommended dosage) * Subject has a HbA1c value (JDS value) between 6.5% and 9.5% and the difference of HbA1c values (JDS value) within ± 1.0% * BMI 20.0 - 45.0 kg/m2 Exclusion Criteria: * Type 1 Diabetes Mellitus * Subject has received insulin within 12 weeks (84 days) before the study * Subject has proliferative diabetic retinopathy * Subject has a history of clinically significant renal disease such as renovascular occlusive disease, nephrectomy and/or renal transplant * Subject with obvious dysuria caused by a neurogenic bladder or a benign prostatic hypertrophy * Subject has a history of cerebral vascular attack, unstable angina, myocardial infarction, vascular intervention, and heart disease (NYHA Class III-IV) within 12 weeks (84 days). Subject has heart disease, cerebral vascular disease which, in the opinion of the principal investigator or the sub-investigator, may interfere with treatment or evaluation of safety of this study. * Female subject who is currently pregnant or lactating, or who is possibly pregnant * Male and pre-menopausal Female subject who cannot use an appropriate contraception during the study * Subject has a history of treatment with ASP1941 * Subject has participated in another clinical study, post marketing study, or medical equipment study within 12 weeks (84 days) before providing written informed consent, or who is currently participating in any of those studies * Subject has a serum creatinine value higher than upper limit of normal range * Subject has a urinary microalbumin/ urinary creatinine ratio \> 300 mg/g in urinalysis * Subject has uncontrolled severe hypertension (subject whose systolic blood pressure is \> 170 mmHg or diastolic blood pressure of \> 95 mmHg measured in a sitting position after 5 minutes of rest * Subject who is judged inappropriate for enrollment into the study by the principal investigator or the sub-investigator