PURPOSE: To cope with the multiplex modulation simply with only one modulation circuit, by FSK or PSK modulation according to the first and second input signals input externally.

CONSTITUTION: In case of FSK modulation, the serial digital signal is input to the first input terminal 1, and a constant signal is input to the second input terminal 2 for selection and switching of two clock signals from the clock oscillator 11 to output FSK wave from the terminal 3. In case of PSK modulation, a constant signal is given to the first input terminal 1 and the serial digital signal is input to the second input terminal 2, and after the selection of PSK clock from the clock oscillator 11, it is added with the phase shift value corresponding to the input serial digital signal from the phase shift circuit 15 at the adder 14 to output PSK wave from the terminal 3.