An object of the present invention is to provide a salt of the compound 1-(2,3-dichlorobenzoyl)-4-((5-fluoro-6-(5-methyl-1H-pyrazol-3-ylamino)pyridin-2-yl)methyl)piperidine-4-carboxylic acid, useful as an antitumor agent, and crystals thereof which are excellent in solubility, stability, and oral absorption and can be produced in large quantities. The present invention relates to a hydrochloride salt of 1-(2,3-dichlorobenzoyl)-4-((5-fluoro-6-(5-methyl-1H-pyrazol-3-ylamino)pyridin-2-yl)methyl)piperidine-4-carboxylic acid and crystals of the hydrochloride salt having characteristic peaks at particular diffraction angles in powder X-ray diffraction spectrum.