Abstract: A booster for a transmission gear box has an actuating rod cooperating with a gearshift lever and a hollow piston rod movably penetrating the pneumatic cylinder and cooperating with the actuating rod. A connector is mounted to the piston rod and introduces and discharges pressurized air into and from the piston rod. A striker is coupled to the actuating and piston rods through a pin and is coupled to a connecting lever of the gear box to allow the connecting lever to be operated in conjunction with the actuating and piston rods. The booster prevents a relative rotating motion between the actuating and piston rods, simplifies the gearshift part of the gear box, smoothly engages and disengages gears to the gear box with a small force and provides an easily-machinable hollow piston rod.