ELECTRONIC KEY SYSTEM

PROBLEM TO BE SOLVED: To enable prompt wireless communication between an electronic key and a vehicle while enabling position determination of the electronic key by using an on-vehicle single transmission antenna, in an electronic key system.SOLUTION: A first request signal Sr1 consists of a region of a first electric field intensity L1 and a region of a second electric field intensity L2 weaker than the first electric field intensity L1. When an electronic key exists in an area outside a vehicle cabin, a signal level in the region of the first electric field intensity L1 becomes equal to or larger than a threshold value Th and a signal level of the region of the second electric field intensity L2 becomes less than the threshold value Th by detection of the first request signal Sr1, whereby the first request signal Sr1 can be recognized. When the electronic key exists in an area inside the vehicle cabin, signal levels of the regions of the first and second electric field intensities L1, L2 become equal to or larger than the threshold value Th by the detection, whereby the signal levels always become high, so that the first request signal Sr1 cannot be recognized.