DECIMATION FILTER

A decimation filter has: a plurality of calculating devices each having a multiplier and an accumulator; a plurality of coefficient memories (a ring memory and shift registers) which store filter coefficients, and which correspond to the calculating devices, respectively; and a selector which sequentially selectively outputs the outputs of the plurality of calculating devices in synchronization with a clock signal. When a decimation ratio is n, filter coefficients which are sequentially shifted by an n number of filter coefficients are read out from the plurality of coefficient memories, and multiplied with a signal in the multipliers of the calculating devices, and results of the multiplications are accumulated in the accumulators to be output.