PURPOSE: To remove completely the influence of a duty change of the clock and to delay correctly at 1/2 symbol by using a clock of a frequency two times as much as the clock inputted to a data symbol generating device.

CONSTITUTION: In a four-phase shift keying/offset four-phase shift keying change-over generating device, a clock frequency inputted to shift registers 11, 12 and 20 is made two times as much as the clock frequency inputted to data symbol generating devices 8 and 9. When the change-over is executed to a four-phase shift keying, a data symbol output is inputted through the same positive edge trigger shift register 12 to a two-phase modulator 4. When the change-over is executed to an offset four-phase shift keying, the second data symbol output passes through the third positive edge trigger shift register 20 and as the result, a 1/2 symbol only is delayed.