Provided is a method for treating damage to the gastric mucosa with a cytoprotective agent, comprising administering to a human in need thereof a pharmaceutical composition comprising an effective amount for treating damage to gastric mucosa of a pharmaceutically acceptable salt of revaprazan as the cytoprotective agent, and a pharmaceutically acceptable carrier. Revaprazan or its salt has an excellent treatment effect for gastrointestinal mucosal damage by potentiating a defensive factor in the gastrointestinal mucosa, simultaneously with acting as an acid pump antagonist.