A mobile device includes a transmitting unit that, each time an ON operation of a switch in a first mode is performed, transmits a wireless signal corresponding to the first mode ON operation by changing a frequency band among three or more frequency bands and that, when an ON operation of the switch in a second mode is performed, transmits a wireless signal, corresponding to the second mode ON operation, in the frequency band selected at that time. The transmitting unit includes a frequency band computing unit that selects one of the three or more frequency bands through a computation for changing a communication environment when the second mode ON operation of the switch is repeatedly performed. A receiver of the in-vehicle device receives a wireless signal transmitted from the transmitting unit and recognizes command information allocated in advance in correspondence with each ON operation mode of the switch.