This mechanism comprises of two spur gears, a rack and pinion, a slider, and a frame. It is designated to generate a constant-speed reciprocating straight line motion. When the spur gear pair is activated by the input crank, the pinion which is attached to one of the spur gears will push the rack and run around its top and bottom. After, since the rack is attached to the slider, the slider will be pushed with a straight line motion based on the force from the pinion. Because the pinion runs around the top and bottom of the rack, the motion direction of the slider will be guided back and forth, which constitutes a reciprocating motion. Besides, if the crank is driven by a constant speed, the output speed of the slider will also be constant.