To quickly determine whether a sealing device is unsealed or not.

A signal transmission control circuit detects whether a lock body is kept in a locked state or an unlocked state. In the locked state, the signal transmission control circuit controls a signal transmission power supply on/off circuit to feed power to a signal transmission circuit from a battery, and a signal is transmitted from the signal transmission circuit. In the unlocked state to the contrary, the signal transmission control circuit controls the signal transmission power supply on/off circuit to feed no power to the signal transmission circuit from the battery, and the signal transmission from the signal transmission circuit is stopped.