1. An angular error detecting device that detects an angular error in a receiving direction of a frequency signal from a tracking target with respect to a front direction of an antenna, based on a phase difference of a first reception signal received at a first receiving unit of the antenna and a second reception signal received at a second receiving unit having a receiving position in the antenna different from a receiving position of the first receiving unit, and the angular error detecting device comprising:a reception signal output unit that outputs a sum signal and a difference signal that are obtained from the first reception signal and the second reception signal to a sum-signal signal path and a difference-signal signal path respectively;
a pilot signal supply unit that superimposes respective pilot signals having aligned phases on the sum signal and the difference signal that are output to the sum-signal signal path and the difference-signal signal path;
a pilot phase difference detection unit that separates the respective pilot signals from a signal that has passed through the sum-signal signal path and a signal that has passed through the difference-signal signal path and detects a phase difference in the separated pilot signals;
a correction unit that performs a correction corresponding to the phase difference in the pilot signals detected at the pilot phase difference detection unit on one side of the sum signal and the difference signal that are obtained via the sum-signal signal path and the difference-signal signal path; and
an angular error detection unit that detects the angular error based on the one side corrected at the correction unit and the other side that is not corrected of the sum signal and the difference signal.