Provided is an array signal processing device capable of, when a spatial averaging method is applied to array signal processing, reducing the number of antennas constituting an array antenna while making use of the spatial averaging method. In the array signal processing device (300), an array antenna (310) comprises four antennas (311-1 to 311-4) disposed at the four vertices of a parallelogram. Correlation calculation units (341-1, 2) calculate, based on a received signal, spatial correlation matrices for respective sub-array antenna (312-1) and sub-array antenna (312-2), the sub-array antenna (312-1) comprising the antennas (311-1, 3) disposed at the opposing two vertices and the antenna (311-2), the sub-array antenna (312-2) comprising the antennas (311-1, 3) and the antenna (311-4). An array rotation unit (342) converts a first spatial matrix of the calculated two spatial matrices to the complex conjugate thereof. A spatial averaging unit (343) averages the complex conjugate of the first spatial matrix and a second spatial matrix.