A vehicle electronic key system includes a control device mounted on a vehicle and an electronic key for transmitting a response signal in response to reception of a request signal from the control device. The control device includes means for outputting a request signal to the electronic key in response to the ON operation of a main switch of the vehicle (request signal generation means, a transmission circuit, and a transmission antenna), means for detecting a response signal from the electronic key (a reception circuit and response signal matching means), and means for performing an alarm output (monitoring means, a third drive circuit, and an alarm lamp) when no response signal is detected in spite of the output of the request signal.