A post-filter includes a microphone array including at least two microphones to which a voice signal are input, a beam former which forms the voice signal input from the microphone array, a divider which divides a target sound containing noise input from the microphone array into at least two frequency bands at a predetermined frequency, a first filter which estimates the filter gain with the noise non-correlated between the microphones, a second filter which estimates a filter gain of one microphone of the microphone array or an average signal of the microphone array, an adder which adds the outputs from the first and second filters to each other, and a unit for reducing the noise based on the outputs from the adder and the beam former.