This study was designed to evaluate the glucose control and hypoglycemic prevention effect of using continuous glucose monitoring system(CGMS) in patients with type 1 diabetes. This is a prospective randomized controlled, single-center clinical study. Patients will randomized 1:1 to either CGMS or conventional self-monitoring of blood glucose (SMBG) group. After 12 weeks of applying the CGMS sensors, the improvement of parameters collected from the CGMS will be estimated in comparison with data collected from the SMBG.

Inclusion Criteria:

1. Male or female patients ages >= 20 years
2. Patients diagnosed with type 1 diabetes.
3. Patients with glycated hemoglobin (HbA1c) > 8.0% within 6 months before screening
4. Patients who agree to perform self blood glucose monitoring responsibly during the study period
5. Patients diagnosed with type 1 diabetes minimum 3 months prior to recruitment

Exclusion Criteria:

1. Patients diagnosed with type 2 diabetes.
2. Patients with chronic disease (Excluding thyroid disorders in which thyroid function is controlled in the normal range), or psychiatric disease
3. Patients who cannot use the device properly such as an illiterate person or foreigners
4. Patients incapable of making decisions based on their own judgement and will
5. A person who may not participate in the study according to investigator's judgement