A transponder which does not require a power source used in an in-wheel motor system and a wheel therewith. The transponder comprises a data transmit/receive antenna, a data transmit/receive section, a sensor circuit, and a sensor power circuit. The sensor power circuit is constituted of a rectification circuit (energy converting means), a storage device and a charging coil and the input side of the rectification circuit is connected to a charging coil and the output side of the rectification circuit is connected to the storage device. The transponder is mounted on a motor rotor provided on an internal surface of a rim section in a tire constituting the wheel, and the charging coil is fixed so as to penetrate through a magnetic field produced by a motor stator.