PURPOSE: To obtain a polyphase PSK modulating wave through digital operation, by obtaining a polyphase carrier wave through the repetition of frequency-division and phase inversion of outputs of an original oscillator, and selecting and outputting the carrier wave with an input digital signal.

CONSTITUTION: In case of, e.g., an octal phase PSK modulator, an original oscillation signal (a), 4f frequency of an oscillator 1 is divided into two, and one branched signal is phase-inverted at a phase inverting circuit 2 to obtain two- phase signals (A), (B) in the relation of phase of (0, π). Further, the signals (A), (B) are 1/2-frequency-divided at frequency dividers 3, 4, each of them is phase- inverted at phase inverting circuits 6 and 7 to obtain signals (D), (E), (C) and (F) having the relation of phase as (0, π/2, π, -π/2). Through the repetition of frequency-division and phase inversion similarly once more, octal phase carrier waves (G)∼(N) are obtained, they are selectively outputted from a switch 15 in response to input data to output the octal phase PSK modulating waves of frequency. 2n phase PSK modulation waves can also be generated through the similar operations.