A wireless device that suppresses deterioration of antenna characteristics and can be made thin is provided. The wireless device is provided with a substrate, a wireless module that is mounted on the substrate and has an antenna unit, and a casing that accommodates the substrate and the wireless module. The wireless device has a gap of a length that is an approximate multiple of a half-wavelength of a radio wave corresponding to a communication frequency of the antenna unit, from the antenna unit toward the casing.