PURPOSE: To enable the common use of a torque spring among engines having a different torque-up ratio from each other, and to enable the fine adjustment of the torque-up rate.

CONSTITUTION: A torque transmitting position adjusting means 17 is provided between a weight side lever 3 and a torque-up main body 10, and the torque-up main body 10 can be moved for adjustment in the longitudinal direction of the weight side lever 3 by this torque transmitting position adjusting means 17. Arm length LT of the lever 3 from a supporting point 16 to a torque-up device 7 can be changed for adjustment, and a pin abutment transmitting surface 15 is formed over the length LC for covering the adjustment area LE of the arm length LT. The gradual torque-up ratio is set by adjusting this arm length LT long, and the steep torque-up rate 18 set by adjusting this arm length LT short.