The purpose of this study is to demonstrate the efficacy of CJ-12420, once daily (QD), compared to esomeprazole in patients with erosive esophagitis classified as Los Angeles (LA) classification grades A to D at Week 8

This is a double blind, randomized, active controlled, phase 3 study. Subjects will be randomly assigned to one of the two treatment groups (CJ-12420 100 mg or esomeprazole 40 mg).

All subjects will be asked to take two tablets at the same time each day throughout the study, and also all subjects will be asked to record daytime and nighttime symptom in a subject diary on a daily basis.

Inclusion Criteria:

1. Subjects aged between 20 and 70 years
2. Subjects who had experienced heartburn and regurgitation within 7 days before visit 1. Entry into study also required that patients had experienced at least mild upper gastrointestinal symptoms on at least 2 days/week or at least moderate upper gastrointestinal symptoms on at least 1 day/week
3. Endoscopically confirmed erosive esophagitis as defined by LA Classification Grading System (A-D) within 14 days prior to randomization
4. Subjects who is able to understand and follow the instructions and is willing to participate throughout the entire study
5. Subjects who voluntarily signed written informed consent form
6. Subjects who agreed to use medically acceptable contraceptives during the period of study.

Exclusion Criteria:

1. Subjects who cannot undergo EGD
2. Subjects who have esophageal stenosis, ulcer stenosis, gastroesophageal varices, Barrett's esophagus, active gastric ulcer, gastrointestinal bleeding or malignant tumor confirmed by EGD
3. Subjects who have warning symptoms of malignant gastrointestinal tract such as odynophagia, severe dysphagia, bleeding, weight loss, anemia, or bloody stool
4. Subjects with eosinophilic esophagitis
5. Subjects diagnosed with primary esophageal motility disorder, IBS, IBD, etc. or with suspected IBS in the last 3 months
6. Subjects who have a history of gastric acid suppression surgery or upper gastrointestinal, esophageal surgery
7. Pregnant or lactating women
8. Subjects with a history of clinically significant hepatic, renal, cardiovascular, respiratory, endocrine and CNS system disorder
9. Subjects with a history of hypersensitivity to the active ingredient or excipients of the study drug, etc.
10. Subjects who participated in the other clinical trial within 4 weeks prior to randomization