To shorten the time necessary for resetting an absorber when performing the next motor vehicle collision test as a braking distance becomes long when the shock absorber provided with a brake shoe is adopted for a device for braking a rectilinearly traveling body which rectilinearly travels by its own inertial force after separated from a motor vehicle to be tested such as a traction pulley for the motor vehicle to be tested in a motor vehicle collision test device and to obtain a brake system for the absorber for the case that two traction pulleys simultaneously travel in a common travel path in the motor vehicle collision test device in which the traction pulleys are arranged in the front and rear of a motor vehicle to be tested.

The kinetic energy possessed by a rectilinearly traveling body which rectilinearly travels by its inertia is converted into the rotational energy of the brake system provided with a strike arm and brake wheel, and the strike arm is provided with a means which does not act on the rehalted rectilinearly traveling body. By this constitution, it is possible to make the braking distance of the rectilinearly travelling body almost zero and to brake two rectilinearly travelling bodies traveling in the same travelling path.