PURPOSE: To output an FM modulated waveform having satisfactory accuracy by equipping the digital FM modulator with a second adder circuit to make the digital value of a clip level correspond to the upper limit and lower limit frequencies of an FM output to be generated from a function ROM.

CONSTITUTION: The FM modulator is composed of a sine wave generating circuit 13 and an offset circuit 14 to determine the offset value of an address signal. An input signal I (m) is inputted to the second adder circuit 22, and the adder circuit 22 adds input digital quantity in which the digital value to which the clip level is given is expressed with ±2n with the output of a first adder circuit 35 and supplies this added output to an integration circuit composed of an adder circuit 23 and a register 24. Further, the digital value of the clip level is made to correspond to the upper limit and lower limit frequencies of the FM output to be generated from a function ROM 21. Thus, the input signal is never compressed, and the deterioration of the accuracy of the FM output can be prevented by controlling the dynamic range of the address signal according to the input signal to express the clip level with the ±2n digital value.