A sound source signal is estimated with high accuracy in a noise environment. A sound source signal estimation unit (15) estimates each sound source signal using a separation matrix from an observation signal obtained by collecting a mixed acoustic signal in which a plurality of sound source signals and diffusive noise are mixed by a microphone array formed by a plurality of microphones The separation matrix is configured to convert steering vectors from each sound source to the microphone into unit vectors and convert a spatial covariance matrix of the diffusive noise into a matrix including a diagonal matrix with a size of the number of sound sources.