PROBLEM TO BE SOLVED: To provide Helicobacter pylori adhesion inhibitor which suppresses adhesion of Helicobacter pylori to gastric mucosa to prevent onset of gastritis, gastric ulcer, gastric cancer, and duodenal ulcer caused by the Helicobacter pylori.SOLUTION: The Helicobacter pylori adhesion inhibitor contains an extract of Japanese horse chestnut seed coat as an active ingredient. The Helicobacter pylori adhesion inhibitor is produced as a pharmaceutical preparation, or can be formed into foods and drinks.