A torque-setting device includes a handle with grooves defined in an internal side, a driving unit attached to the handle, a strain gauge connected to the driving unit, a strain spring abutted against the strain gauge, a nut abutted against the strain spring, an axle and a knob. The axle includes a thread. The thread is engaged with the nut. The knob includes a tooth on an external side. The knob is operable to rotate the axle relative to the nut, thus moving the nut relative to the strain spring to set a value of torque. The knob is movable between a first position where the tooth is inserted in one of the grooves to retain the value of torque and a second position where the tooth is removed from the grooves to allow the rotation of the knob and therefore the rotation of the axle.