This electronic key system 1 comprises: an electronic key 10 which is enabled to engage in radio communication with a vehicle 20 on condition that a vibration is detected by a vibration detection part 14; and the vehicle 20 which has an on-board control part 21 for starting an engine 25a on condition that the radio communication with the electronic key 10 is established, and a push switch 24 installed in the vehicle is operated. The on-board control part 21 causes the vehicle to be vibrated by the engine 25a on condition that the push switch 24 is operated.
