The invention discloses a gear box especially used for a motor vehicle with a retractable load bearing arm. The gear box is suitable for driving motions for directly or indirectly delivering an internal combustion motor (M) by at least one front or rear axle arranged with a driven pulley. The gear box comprises a shell (13) containing an angle-shaped transmission device (15); the angle-shaped transmission device is distributed into a drive shaft which transmits the motion of the output shaft (17) of a motor to the front shaft or rear shaft or the driving shaft (9 or 10) of the front shaft and the rear shaft. The gear box comprises a run-through shaft (16) output through power, which is distributed into a pump which drives to generate hydraulic pressure energy or fluid static pressure energy.