To provide a duty adjustment circuit capable of easily obtaining a desired duty when the duty of an input is changed.

The duty adjustment circuit is provided with: an AC coupling circuit 11 for passing an AC component of a signal S1; a bias circuit 21 including a voltage setting means having a p-MOS 23, an n-MOS 25 and a division resistor 27 and a multiplexer 33 connecting its input to the output of the division resistor 27 and outputting the voltage of a selected node 29 through an output resistor 37, and connecting the output of the multiplexer 33 to the output of the AC coupling circuit 11; and a waveform shaping circuit 41 for inputting a signal S 2 from the output of the AC coupling circuit 11 to which a DC bias component from the bias circuit 21 is added and outputting a shaped signal S3.