To provide an impact energy absorption type underrun protector capable of sufficiently easing an impact received by another vehicle even in the case of a collision in which input load is small.

A front underrun protector 5 is extended in the vehicle width direction below the front end of a main frame 3 of a vehicle 1. An energy absorption body 7 has one end fixed to the rear surface of the front underrun protector 5 and is extended from the one end to the rear of the vehicle. A front underrun protector bracket 6, which is fixed to the other end of the energy absorption body 7, supports the front underrun protector 5 on the main frame 3 via the energy absorption body 7. The energy absorption body 7 is deformed by being crushed in the vehicle longitudinal direction receiving load from the vehicle longitudinal direction and has load-displacement characteristics in which increase in a deformation amount thereof and increase in load are almost proportional.