The purpose of this study is to investigate the superiority of efficacy of TAK-438, once daily (QD), to placebo in patients with non-erosive gastroesophageal reflux disease.

Inclusion Criteria:

1. Participants with grade N or M in the modified LA classification system confirmed by endoscopy at initiation of the pre-observation period (VISIT 1).

2. Participants with repeated acid reflux symptoms (heartburn or regurgitation) for 2 days or more in one week in the 3 weeks before initiation of initiation of the pre-observation period (VISIT 1).

3. Participants with severity* of moderate or higher for acid reflux symptoms (heartburn or regurgitation) in the 3 weeks before initiation of the pre-observation period (VISIT 1)

   * Severity: No symptoms, very mild (symptoms present but often forgotten), mild (not so painful), moderate (rather painful), severe (painful) and very severe (painful enough to affect night time sleep or daily activities)

4. Outpatients (hospitalization for testing possible)

Exclusion Criteria:

1. Participants with an esophagus-related complication [Barrett's esophagus (3 cm or more, LSBE), eosinophilic esophagitis, esophageal varices, scleroderma, viral or fungal infections, esophageal stenosis, etc.], or a history of radiotherapy or cryotherapy of the esophagus, a caustic or physiochemical trauma (esophageal sclerotherapy, etc.). However, participants with Barrett's esophagus (less than 3 cm, SSBE) or Schatzki's ring (mucosal tissue ring around inferior esophageal sphincter) are allowed to be included.
2. Participants who have received surgery or treatment affecting gastroesophageal reflux (cardioplasty, dilation of esophageal stenosis [excluding Schatzki's ring], etc.), or who have a history of surgery of stomach or duodenum (excluding removal of benign polyp under endoscopy)
3. Participants who have acute upper gastrointestinal bleeding, gastric ulcers (mucosal defects associated with white coating) or duodenal ulcers (mucosal defect with white coating) within 30 days before initiation of the pre-observation period (VISIT 1) However, participants with gastric or duodenal erosions are allowed to be included.
4. Participants with acute gastritis or acute exacerbation of chronic gastritis as a complication
5. Participants with a previous or current history of the Zollinger-Ellison syndrome or other gastric acid hypersecretion disorders
6. Participants with a history of chest pain due to heart disease or with chest pains suspected of being caused by heart disease within one year before initiation of the pre-observation period (VISIT 1)