To provide an electronic key system capable of creating an area boundary in close vicinity to an antenna, an electronic key position detector, and a method for detecting a position of an electronic key.

A rotational electromagnetic field generating unit 17 generates such a rotational electromagnetic field as to make an aspect in the direction of the rotational electromagnetic field changed in such a manner that an area boundary serves as a boundary. The rotational electromagnetic field generating unit 17 includes a bipolar electromagnetic field generating unit 13 which generates a bipolar electromagnetic field, and a quadrupole electromagnetic field generating unit 14 which generates a quadrupole electromagnetic field different in phase from the bipolar electromagnetic field. An electromagnetic field direction detecting unit 21 detects an electromagnetic field direction to output a signal for giving notice to an electronic key position detector 1. A position detecting unit 15 detects a position of an electronic key 2 on the basis of the electromagnetic field direction detected by the electronic key 2.