1. A frequency modulation radar device, comprising: transmitting means for transmitting a transmitting signal that has been modulated in frequency so as to change a frequency at a constant change rate with time; M receiving means for receiving a reflected signal resulting from reflecting the transmitting signal by a target object as M channels, where M is an integer of 2 or larger; mixing means for mixing the transmitting signal with the M received signals, respectively, to obtain beat signals for the M channels; frequency analyzing means for analyzing the beat signals for the M channels in frequency; and calculating means for calculating a distance to the target object and an orientation angle based on frequency analysis results for the M channels, wherein the calculating means calculates a noise level from the frequency analysis result for the M channels, extracts a peak signal of a subject target object in each of the channels based on the calculated noise level to generate a covariance matrix of M×M order, discriminates between a signal eigenvalue corresponding to the target object and a noise eigenvalue corresponding to noises among M eigenvalues of the covariance matrix based on the noise level, estimates the number of incident signals K, where K is an integer that is equal to or larger than 1 but smaller than M, from the number of the discriminated signal eigenvalues, and calculates the orientation angles of the respective K incident signals to estimate the orientation angle of the target object.