PURPOSE: To obtain an arbitrary attenuation to a signal with an arbitrary amplitude, by sampling an input signal with a control signal and changing the attenuation of the signal through the variable duty cycle.

CONSTITUTION: A signal is applied to a switch circuit 12 from an input terminal 11. The circuit 12 is switched with a control signal from a duty varying circuit 15 and the signal is sampled with the circuit 12. This signal is applied to a low pass filter 13 and a signal attenuated with the sampling is obtained at an output terminal 17. A pulse signal generating circuit 14 generates a pulse signal with a prescribed period, which is applied to the circuit 15. The circuit 15 can arbitrarily set the duty cycle of the pulse signal and the pulse signal in which the duty cycle is selected to a desired value controls the switching of the switch circuit 12 and samples the signal applied to the circuit 12.