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 , means for detecting a response signal from the electronic key , and means for performing an alarm output when no response signal is detected in spite of the output of the request signal .