A method for producing crystal A of 2-(3-cyano-4-isobutyloxyphenyl)-4-methyl-5-thiazolecarboxylic acid by dissolving 2-(3-cyano-4-isobutyloxyphenyl)-4-methyl-5-thiazolecarboxylic acid in methanol or a mixed solvent of methanol and water (the volume ratio of methanol to water is 90/10 or more), then adding water until the ratio of methanol to water becomes 7/3, and further adding a specific amount of a seed crystal at a specific timing during the addition of water.
