This study is designed as a prospective, multi-centre, parallel group, double-blind randomized, placebo-controlled, phase 3 clinical study to evaluate the efficacy and safety of MP-513 (Teneligliptin) in combination with metformin.

Inclusion Criteria:

• A signed and dated informed consent form obtained from the subject, in accordance.
• The subject is aged ≥18 years at signature of the informed consent form.
• Hospitalization status: outpatient.
• The subject has a documented diagnosis of type 2 diabetes mellitus for at least 3 months at the screening visit (Day -28).
• The subject's type 2 diabetes mellitus is managed by metformin monotherapy ≥1000 mg/day plus diet and exercise therapy, and the dosage or dose regimen of metformin and diet and exercise regimen has not been changed for at least 8 consecutive weeks at the screening visit (Day -28). Subjects who cannot do exercise due to complication are not limited to this criteria.
• The subject's HbA1c is ≥ 7.0% and < 10.0% at the screening visit (Day -28) and on Day -14.

Exclusion Criteria:

• The subject has a history of type 1 diabetes mellitus or a secondary form of diabetes.
• The subject has received insulin within 1 year prior to the screening visit (Day -28), with the exception of insulin therapy during hospitalization or insulin therapy for medical conditions not requiring hospitalization (< 2 weeks' duration).
• The subject has received an anti-diabetic drug within 8 weeks prior to the screening visit (Day -28).

FAS: All subjects in the randomized set who have received at least one dose of study medication during the double-blind treatment period and have at least one post-baseline efficacy observation. Subjects who were not diagnosed with type 2 diabetes mellitus were excluded.

24 weeks

All subjects in the randomized set who have received at least one dose of study medication during the double-blind treatment period. One subject who had been randomized in placebo group was handled as Teneligliptin group, because the subject had been administered Teneligliptin mistakenly.