A signal processing circuit detects, at a plurality of different timing points, a first and a second distance of an oncoming vehicle approaching a vehicle including the radar apparatus and detects a first and a second component of a relative velocity of the vehicle in the radar-apparatus direction. A distance of closest approach of the oncoming vehicle to the vehicle appears when the vehicle and the oncoming vehicle pass each other side by side. The signal processing circuit computes the distance of closest approach on the basis of a formula indicating that a relative velocity given by the first distance, the distance of closest approach, and the first component of a relative velocity in the radar-apparatus direction is equal to a relative velocity given by the second distance, the distance of closest approach, and the second component of a relative velocity in the radar-apparatus direction.