Electronic key system

An electronic key system (1) that reduces the time for locating an electronic key from responses from the electronic key sought for by requests from LF transmitters (22, 23). The electronic key system checks a combination of responses from the electronic key to perform ID verification. The electronic key system includes a key location determination unit (21b) that forms a driver side communication area (Ad) when a request switch (26) is operated to perform exterior determination and determine whether the electronic key is located outside a vehicle based on a response from the electronic key in the driver side communication area (Ad). Then, the key location determination unit forms a passenger side communication area (Ap) to perform interior determination and determine whether the electronic key is located inside the vehicle based on responses from the electronic key in the driver and passenger side communication areas (Ad, Ap).