Speed-change device for drill machine

A speed-change device for a drill machine, wherein the drill machine includes a drive motor having a spindle, a cutter connective shaft and a shell member, the device comprising:

• an active disc unit installed to the spindle and including a first wedged disc and a second wedged disc paired to the first wedged disc;
• a driven disc unit installed to the cutter connective shaft and including a first wedged disc and a second wedged disc paired and coupled to the first wedged disc;
• a belt wound around the active disc unit and the driven disc unit, with the active disc unit driving the driven disc unit to operate via the belt;
• and
• an driven operating unit installed to the shell member and including a driven element and a pressing element which is fixed to the shell member and includes a fulcrum, an operating portion and an adjusting portion abutted against the driven disc unit, with the driven element, which is provided on the shell member and not coaxial to the spindle, inserted to the adjusting portion and driving the adjusting portion to move longitudinally with respect to the shell member, with the operating portion moving with respect to the driven element simultaneously, and driving the first and second wedged discs of the driven disc unit to attach to/detach from each other.