To allow a user to receive a radio signal of a portable machine securely.

The smart keyless entry system is composed of an on-board machine 100 loaded on a vehicle and the portable machine 200 carried by an occupant to control on-vehicle control equipments 50, 52, 54 by receiving the radio signals from the portable machine 200 by the on-vehicle machine 100. The on-board machine 100 has a receiving antenna 1042 for receiving the radio signals from the portable machine 200, a receiving circuit 1044 for demodulating the radio signals received by the receiving antenna 1042 into electric signals, a matching circuit 1046 for matching impedance of the receiving antenna 1042 and impedance of the receiving circuit 1044 mutually, a voltage detecting means 1048 for detecting the electric signal demodulated by the receiving circuit 1044, and a matching optimizing means 1050 for optimizing mutual matching of impedance of the receiving antenna 1042 and impedance of the receiving circuit 1044 by controlling the matching circuit 1046 based on the voltages detected by the voltage detecting means 1048.