To provide a keyless entry system which conducts suitable lock and unlock operation according to the current position of an operator and holds down the power consumption of a portable machine to the minimum.

In transmitting a radio signal from a portable machine having a GPS receiver to an on-vehicle machine, it is judged whether the distance D between the stop position P1 of an automobile obtained from a received GPS signal and the current position P2 is shorter than a designated value or not (S127-S130), and if YES (distance D < designated value), a first unlock signal is sent out with field strength K1 or K2 to instruct the on-vehicle machine to perform lock operation (S133-S137).