In a case where a relative velocity Vr decreases, a timing calculation unit of a collision-avoidance support ECU calculates a time T1 shorter than a time T2, as a time to a collision, using a distance D and the relative velocity Vr without using acceleration Gr. The timing calculation unit calculates a timing of a start of collision-avoidance support on the basis of the time T1. In a case where the relative velocity increases, the timing calculation unit calculates the time T2 shorter than the time T1, as a time to a collision, using the distance D, the relative velocity Vr and the acceleration Gr. The timing calculation unit calculates the timing of a start of collision-avoidance support on the basis of the time T2.