An object of the present invention is to provide a salt compound of 4-(2-fluoro-4-(3-(2-phenylacetyl)thioureido)phenoxy)-7-methoxy-N-methylquinoline-6-carboxamide, which is useful as an antitumor agent, and crystal of the salt. The salt and the crystal are excellent in terms of solubility, stability, and peroral absorbability and can be mass-produced. The present invention relates to: a mesylic acid salt of 4-(2-fluoro-4-(3-(2-phenylacetyl)thioureido)phenoxy)-7-methoxy-N-methylquinoline-6-carboxamide; and the mesylic acid salt including a crystal which gives an X-ray powder diffraction spectrum having characteristic peaks at specific diffraction angles.