The purpose of this study is to compare the treatment effects of rabeprazole and lansoprazole depending on the genotyping (process of determining the genetic constitution) of CYP2C19 in treating reflux esophagitis (caused by gastroesophageal reflux; deterioration of the protective lining on the inner wall of the lower esophagus); and to evaluate the cure rate of reflux esophagitis on endoscopy (a thin flexible tube with a microscopic camera at the end which is passed down your throat into the esophagus, stomach, and duodenum) after treatment with rabeprazole and lansoprazole.

This is a prospective (study following participants forward in time), open-label (all people know the identity of the intervention), multi-center (conducted in more than 1 center), randomized (study drug assigned by chance) study in participants with reflux esophagitis. The study will include 4 visits: Visit 1 (Screening period of up to 14 days), Visit 2 (Day 1), Visit 3 (Day 29+3), and Visit 4 (Day 56). After Screening, eligible participants will be analyzed on Visit 2 (Day 1) for symptoms during past week, At visit 3 (Day 29+3) participants will be randomly assigned to 1 of the 2 treatment groups: rabeprazole 20 milligram (mg) or lansoprazole 30 mg group. Participants will receive rabeprazole 20 mg tablet orally once daily for 28 to 56 days or lansoprazole 30 mg capsule orally once daily for 28 to 56 days. A post-study follow-up visit will be conducted only if participant will be affected by any serious adverse event within 30 days after the completion of study drug. Participants will primarily be assessed for the cure rate of reflux esophagitis based on endoscopy of 2 groups. Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Participants diagnosed with reflux esophagitis of Grade A or higher by Los Angeles (LA) classification based on the endoscopy among participants complaining of gastroesophageal reflux symptoms (such as: Heartburn, regurgitation, globus sensation, chronic [lasting a long time] cough [sudden, loud flow if air from the lungs], epigastric [area above the navel] pain, non-cardiac chest pain, hoarseness, or dysphagia), or those who diagnosed with reflux esophagitis of Grade B or higher without complaining of symptoms
• Participants without other serious disease except the study indication (reflux esophagitis)
• Participants with hematology (related to blood) panel, serum chemistry panel, or urinalysis result clinically within twice the normal range
• Female Participants of child-bearing potential who are using the appropriate contraceptive or with a negative urine pregnancy test

Exclusion Criteria:

• Participants with other serious gastrointestinal disease except reflux esophagitis (example: digestive tract cancer [abnormal tissue that grows and spreads in the body until it kills], hepatic disease, pancreatic disease, and ulcer. However, the scar of an ulcer is included in study targets
• Participants with other serious concomitant disease(s) such as renal disorder, cerebrovascular disease, cardiovascular disease, hepatic disease, and severe respiratory disease
• Participants with medical history of upper gastrointestinal tract surgery, esophagostenosis, or a chalasia
• Participants with hematology panel, serum chemistry panel, or urinalysis result of above twice the normal range
• Participants who cannot discontinue proton pump inhibitors or Histamine 2 antagonist which may have influence on the study, 4 weeks before the start of this clinical study