An acoustic signal is separated based on a difference in the distance from a sound source to a microphone. By using a filter obtained by associating a value corresponding to an estimated value of a short-distance acoustic signal which is obtained by using “a predetermined function” from a second acoustic signal derived from signals collected by “a plurality of microphones” and is emitted from a position close to “the plurality of microphones” with a value corresponding to an estimated value of a long-distance acoustic signal which is emitted from a position far from “the plurality of microphones”, a desired acoustic signal representing at least one of a sound emitted from a position close to “a specific microphone” and a sound emitted from a position far from “the specific microphone” is acquired from a first acoustic signal derived from a signal collected by “the specific microphone”. Note that “the predetermined function” is a function which uses such an approximation that a sound emitted from the position close to “the plurality of microphones” is collected as a spherical wave, and a sound emitted from the position far from “the plurality of microphones” is collected as a plane wave.