signal processing device comprising: a mixed acoustic signal acquisition part that acquires a mixed acoustic signal including a plurality of acoustic signals; a mixed feature amount conversion part that converts the mixed acoustic signal into a mixed feature amount indicating a feature of the mixed acoustic signal; a mask estimation part that estimates a plurality of masks corresponding to each of the plurality of acoustic signals based on the mixed feature amount; an acoustic signal conversion part that calculates a plurality of separated feature amounts corresponding to each of the plurality of acoustic signals from the mixed feature amount by using the plurality of masks, and converts the plurality of separated feature amounts that are calculated into a plurality of separated acoustic signals; an environment sound section estimation part that estimates an environment sound section including only an acoustic signal indicating an environment sound in all input sections of the mixed acoustic signal based on the plurality of separated acoustic signals; an environment acoustic signal extraction part that extracts, as an environment acoustic signal, the mixed acoustic signal in the estimated environment sound section from the mixed acoustic signal; and an environment sound feature amount conversion part that converts the environment acoustic signal into an environment sound feature amount indicating a feature of the environment acoustic signal, wherein the mask estimation part weights the mixed feature amount by using the environment sound feature amount, and estimates the plurality of masks based on the weighted mixed feature amount. a mixed acoustic signal acquisition part that acquires a mixed acoustic signal including a plurality of acoustic signals; a mixed feature amount conversion part that converts the mixed acoustic signal into a mixed feature amount indicating a feature of the mixed acoustic signal; a mask estimation part that estimates a plurality of masks corresponding to each of the plurality of acoustic signals based on the mixed feature amount; an acoustic signal conversion part that calculates a plurality of separated feature amounts corresponding to each of the plurality of acoustic signals from the mixed feature amount by using the plurality of masks, and converts the plurality of separated feature amounts that are calculated into a plurality of separated acoustic signals; an environment sound section estimation part that estimates an environment sound section including only an acoustic signal indicating an environment sound in all input sections of the mixed acoustic signal based on the plurality of separated acoustic signals; an environment acoustic signal extraction part that extracts, as an environment acoustic signal, the mixed acoustic signal in the estimated environment sound section from the mixed acoustic signal; and an environment sound feature amount conversion part that converts the environment acoustic signal into an environment sound feature amount indicating a feature of the environment acoustic signal, wherein the mask estimation part weights the mixed feature amount by using the environment sound feature amount, and estimates the plurality of masks based on the weighted mixed feature amount.