To provide an operation support system for avoiding more exactly that a backward vehicle hits a front vehicle from behind.

The operation support system: measures a distance between a surrounding vehicle and an own-vehicle by a millimeter wave radar 10; receives by a receiver 40 of the own-vehicle, speed of the surrounding vehicle detected by a vehicle speed sensor 110 of the surrounding vehicle and transmitted by a transmitter 140; and computes relative speed of the surrounding vehicle and the own-vehicle from received surrounding vehicle speed and the own-vehicle speed detected by a vehicle speed sensor 12 of the own-vehicle. When a distance between the surrounding vehicle is less than a predetermined distance and when relative speed with the surrounding vehicle is over the predetermined value, an alarm display request is given to the surrounding vehicle through a transmitter 70. Receiving the alarm display request with a receiver 100, the surrounding vehicle performs alarm display to the own-vehicle by a brake indicating lamp 150 or a stop lamp 152.