To control interference of answerback signals sent from a plurality of portable machines receiving a request signal sent from a vehicle.
When a sheet switch 7 is in an off state, a controller 2 carried on a vehicle sends a request signal through a transmission circuit 5 and antenna coils 8 to 11. When receiving the request signal with a reception circuit 20, a portable machine 3 sends an answerback signal made up by arranging three blocks of a control signal where more than one control signal frame containing an ID code with an interval are arranged continuously, through a transmission circuit 21 and an antenna 25. The number of control signal frames of each control signal block and an interval are set randomly every time when a request signal is received.
MIZUNO HIROMITSU
SHIBAGAKI YUJI
MAEDA TORU
YAMAMOTO KEIJI
TOYOTA MOTOR CORP