A radar apparatus generates a spectrum distribution where frequencies in a beat signal are associated with intensities of respective frequency components. Based on a plurality of spectrum distributions generated over a predetermined number of measurement cycles prescribed in advance, the radar apparatus generates a reflection intensity distribution where frequencies are associated with road surface reflection intensities of the radar wave from a road surface at each frequency. In the reflection intensity distribution, the radar apparatus detects an intensity peak indicating a frequency that maximizes the road surface reflection intensity. Based on the detected intensity peak, the radar apparatus determines at least whether or not the radar apparatus is in an axis deviation state that is taken as a state where a reference axis of the radar apparatus has an inclination of not less than a prescribed angle in a vehicle height direction relative to a horizontal axis prescribed to a vehicle.