PURPOSE: To reduce the circuit scale of the voice base band multiplex system decoder by the MUSE system.

CONSTITUTION: A voice input signal (voice digital input) (j) is given to an LPF 51 whose coefficient is variable while being controlled by a tetral counter 52. The LPF 51 is made up of a D flip-flop 61, each coefficient device 62 with tap coefficients 0,β0-β8, a changeover device 63 and a total adder 64. Each coefficient device 62 is made up of a bit shifter 21 and an adder 22. The bit shift device 21 shits right each of input data strings y1-y8 by bit number corresponding to a digit of the tap coefficients β0-β8 which is set to '1'. The adder 22 adds totally shift results of the bit shifter 21.