To provide an electronic key system which wirelessly transfers electric power to a portable machine, and can form a stable communication area and also can secure crime prevention.

A reception area Avv of a drive radio wave Svv as a radio signal in a UHF band is set to protrude to the outside of a specified communication area Ar so that its null point Pn can be positioned in a boundary Lbrd of the specified communication area Ar. Additionally, a reception area Arq of a response request signal Srq as a radio signal in an LF band is set to correspond to the specified communication area Ar. An area where the reception area Avv of the drive radio wave Svv and the reception area Arq of the response request signal Srq overlap each other is set as an actual communication area Ap where the portable machine and the vehicle communicate with each other.

COPYRIGHT: (C)2011,JPO&INPIT