PURPOSE: To obtain an easy-to-control filter having no reduction of the general impedance, by actuating plural filters connected in parallel in a seccessive switching by the time division.

CONSTITUTION: The input signal is supplied to the input terminal 9, and the PIN diodes 5a∼5n conduct successively with the outputs of the output terminals 22a∼ 22n of the ring counter 21. In other words, the input signal is applied successively to one of the filters 1a∼1n, and the output of the filter is delivered to the mixer 17. Then the frequency of the oscillator 24 is made double as high as the frequency of the input signal, and as a result the output of the characteristics same as that obtained through the filters 1a∼1n connected in parallel can be obtained at the terminal 19.