PURPOSE: To improve the calling efficiency, by advancing a collating step independently of an output of a collating circuit depending on a preamble signal with an input of a control signal and attaining the omission of a preamble code.

CONSTITUTION: An NRZ signal transmitted converted and detected at a radio section 6 and transmitted sequentially to the collating circuit 11 via a bit synchronizing circuit 7. Further, a signal subjected to bit-synchronism at a timing phase adjusting circuit 10 is inputted to a frame bit timing circuit 12 to drive a preamble signal generating circuit 13. When a preamble pattern is collated at the collating circuit 11, an H signal is transmitted to a preamble flag circuit 14 to drive the frame bit timing circuit 12. Further, a control signal 27 brings an output of an OR circuit 26 to H independently of an output of the collating circuit 11.