The present invention aims to provide a stable form of (R)-2-{3-[1-(acenaphthen-1-yl)piperidin-4-yl]-2,3-dihydro-2-oxo-benzimidazol-1-yl}-N-methylacetamide, which is free of problems of water adsorption and the like, and shows superior water solubility.The present invention provides a crystal and a salt of (R)-2-{3-[1-(acenaphthen-1-yl)piperidin-4-yl]-2,3-dihydro-2-oxo-benzimidazol-1-yl}-N-methylacetamide in a crystal form.