A prevention section generates a prevention signal by performing an interference removal process of preventing an influence of radio wave interference with respect to a non-prevention signal acquired by an acquisition section from a radar sensor for each processing cycle. An analysis section performs a frequency analysis process by using the prevention signal when an operation mode is an interference mode and by using the non-prevention signal when the operation mode is a normal mode. A determination section determines, based on an analysis result obtained by the analysis section, whether radio wave interference is present. When the operation mode is the normal mode and the interference is determined to be present, a switching section switches the operation mode to the interference mode, maintains the interference mode during a certain number of processing cycles, and then switches the operation mode to the normal mode.