Provided is a novel cyclic sulfonium salt compound which is useful for the prevention or treatment of diabetes and the like. The present invention relates to a novel cyclic sulfonium salt compound represented by general formula (I) or (II), an isomer or solvate of the compound, or a pharmaceutically acceptable salt of the compound or the isomer or solvate. The present invention also relates to an α-glucosidase inhibitor, a pharmaceutical composition for preventing or treating diabetes, and an anti-diabetes food, each of which comprises the compound represented by general formula (I) or (II) and the like.
