In a radar apparatus, one frequency pair is extracted from among all frequency pairs, and an eigenvalue ratio in relation to the extracted pair is derived. The number of incoming waves is estimated according to the number of eigenvalue ratios each of which is not less than a reference threshold. Then, a proportion of the frequency pairs each estimated to have a plurality of incoming waves, relative to all frequency pairs (hereinafter referred to as plural detection proportion) is calculated as an evaluation value. These steps are repeated every time radar waves are transmitted and received. As a result, when a state where the plural detection proportion becomes not less than a specified proportion is detected over a specified number of cycles, it is determined that noise factor materials have adhered to a covering member.