1. An electronic scanning radar apparatus mounted on a moving object, comprising: a receiving unit configured to include a plurality of antennas receiving a received wave arriving from a target having reflected a transmitted wave; a beat signal generating unit configured to generate beat signals from the transmitted wave and the received wave; a frequency resolving unit configured to resolve the beat signals into beat frequencies having a predetermined frequency bandwidth and calculate complex data based on the resolved beat signals for each beat frequency; and an azimuth detecting unit configured to estimate a wave number of the received wave based on an eigenvalue being a component part of a normal equation having complex data as elements calculated based on the beat signals, create a coefficient calculated as a solution of a normal equation of a signal subspace formed based on eigenvalues and eigenvectors corresponding to a number of the estimated wave number, and calculate a DOA of the received wave based on the created coefficient.