Electronic key system

An electronic key system comprising:

• a vehicle-mounted device mounted to a vehicle;
• and
• a plurality of electronic keys each wirelessly communicable with the vehicle-mounted device,
• wherein the electronic key system is configured to have:
• a normal mode in which a given processing is permitted to be executed by the vehicle-mounted device when a given wireless communication processing between the vehicle-mounted device and any one of the plurality of electronic keys is successfully completed;
• and
• a deactivated mode in which the given processing is inhibited from being executed by the vehicle-mounted device,
• wherein each of the plurality of electronic keys is configured, when operating in the deactivated mode, to transmit, at a given time, a signal containing deactivated mode information indicating that a corresponding electronic key is operating in the deactivated mode, and
• wherein each of the plurality of electronic keys is configured, when operating in the normal mode, to be shifted to the deactivated mode in response to receiving of the signal containing the deactivated mode information so as to transmit, at the given time, the signal containing the deactivated mode information.