PURPOSE: To stabilize operations when input signals are stopped, by providing an FF, which is inverted at every clock when the logic of a control terminal indicating presence and absence of input delta modulation signals indicates an input signal absence state, and a delta modulation code decoder.

CONSTITUTION: When a delta modulation code is inputted to terminal 8 and control terminal 9 is high-potential, AND circuit 12 is opened, and circuit 11 is closed, and input signals are inputted to the D input of FF 15 through OR circuit 13, and FF 15 shapes the waveform of them and transfers them to decoder 5. When input signals are stopped, terminal 9 becomes low-potential, and circuit 11 is opened, and circuit 12 is closed, and the Q inversion output is inputted to the D terminal of FF 15, and 0 and 1 are alternately inputted to decoder 5 repeatedly as the output of FF 15 at every clock input of terminal 10. As a result, the output of decoder 5 does not reach a saturation point, and a click sound generated when input signals are stopped is eliminated, thus performing stable operations.