Inclusion Criteria:
1. Patients ≥19 and ≤ 80 years of age at Visit 1 (Screening) in accordance with American Diabetes Association (ADA) guidelines
2. Patients who had received a stable dose of Drug A for at least 8 weeks prior to Visit 2 (Run-in vis it).
3. In case of antidiabetic concomitant medications, patients who have maintained up to 2 oral antidiabetic drugs \[OADs\]) without changing regimen/dose/dosage at least 8 weeks prior to Visit 2 (Run-in visit).
4. Patients with FPG of \<270 mg/dL at Visit 1 (Screening) (FPG result at Visit 1 will use local laboratory results)
5. Body Mass Index (BMI) 18.0-40.0 kg/m2.
Exclusion Criteria:
1. Patients with type 1 diabetes mellitus (T1DM), congenital diabetes mellitus (DM), or secondary diabetes as follows:
1. Diabetes caused by Cushing's syndrome and acromegaly.
2. Patients with fasting C-peptide \<0.70 ng/mL (0.23 nmol/L) are excluded if the Investigator cannot rule out T1DM based on the clinical assessment.
3. Patients with a history of T1DM or a history of ketoacidosis or patients assessed by the Investigator as possibly having T1DM confirmed with a C-peptide \<0.70 ng/mL (0.23 nmol/L).
4. History of other specific types of diabetes (eg, genetic syndromes, secondary pancreatic diabetes, diabetes due to endocrinopathies, drug- or chemical-induced, and post-organ transplant).
2. Patients receiving SGLT2 inhibitors, GLP-analogues, thiazolidinediones, or sulfonylureas (at Screening and Run in).
3. At Visit 1 (Screening), patients with a history of the following:
1. Patients who had experienced severe hypoglycemia within 24 weeks prior to Screening or who had experienced hypoglycemia at least 3 times a week within 8 weeks prior to Screening.
2. Patients with a history of diabetic ketoacidosis or coma from hyperosmolar hyperglycemic syndrome within 24 weeks.
3. Patients with a history of myocardial infarction, unstable angina, arterial revascularization, stroke, transient ischemic attack, within 3 months prior to Screening.
4. Patients with New York Heart Association (NYHA) Class III, IV congestive heart failure or arrhythmia requiring treatment. History of dose modification of a treatment for thyroid dysfunction within the past 6 weeks (If patients have been on a stable dose from before enrollment to the study, concomitant administration is allowed. Dose reduction for stable condition is allowed).
5. Patients who had a surgical operation within 4 weeks (excluding minor surgeries without restriction on food and fluid intake) or who are scheduled to have a significant surgery during the study period.
6. Patients with pituitary insufficiency or adrenal insufficiency.
7. Patients with pulmonary embolism, severe pulmonary dysfunction, or who are susceptible to be accompanied by hypoxemia at Screening.
4. Patients who are on or likely to require treatment for ≥14 consecutive days or repeated courses of pharmacologic doses of corticosteroids.
