PURPOSE: To prevent the generation of harmonics produced at switching of a data signal, by inserting a filter in a control signal path of a switching device which starts and stops the transmission data.

CONSTITUTION: In a transmission logical circuit 4 of a burst signal A, an output of a modulator 2 controls a modulation signal so as not to produce 2-symbol phase inversion at the start and end of burst. The burst signal A is limited for the band through a low-pass filter 5 and inputted to a control signal terminal of a switching device 3. A data signal B from the modulator 2 is switched and transmitted with the burst signal limited in terms of band by the switch 3.