A switch device is provided that ensures formation of a communicable area by a coil antenna. The switch device includes an ignition switch operated by an operator for driving an engine starter, a decorative cap arranged to surround the ignition switch and having an ornamental surface, and the coil antenna arranged adjacent to the decorative cap for transmitting a transponder-driving radio wave. The decorative cap includes a transmittable area that can transmit the transponder-driving radio wave therethrough. The transmittable area is formed in a part of the decorative cap excluding the ornamental surface.