A collision reducing device including a radar, an image sensor, a collision mitigation, and a brake. A collision predicting section of the collision mitigation has a first actuating section for causing a vehicle control section to perform running control when a collision possibility exceeds a reference value in one-frame determination, a second actuating section for causing the vehicle control section to perform running control when the collision possibility exceeds a reference value in M-frame determination, and a selecting section for selectively operating the first actuating section and second actuating section, so that the vehicle control section can be operated by two kinds of numbers of determinations, whereby the speed of collision determination can be secured by a smaller number of determinations when operating the first actuating section, while malfunctions can be reduced more by a greater number of determinations when operating the second actuating section.