PURPOSE: To obtain an arbitrary frequency characteristic by cascading characteristic circuits having differential and integral characteristics and connecting weighting circuits to input and output terminals and adding their outputs by an adding circuit.

CONSTITUTION: Differentiating circuits 111 and 112 and an integrating circuit 121 are cascaded, and weighting circuits 210∼213 are connected to the input terminal and respective output terminals of these circuits, and outputs of circuits 210∼213 are added by an adding circuit 31. The weight of a filter 1 is set to values U0∼U3 obtained in accordance with formulas I to obtain the filter having a desired frequency characteristic. In formulas I, α1∼α3 are constants determined by characteristics of differentiating and integrating circuits and a0, b0, c0 and d0 are constants obtained in accordance with formulas II.