The invention provides an automatic loading device used for machining and preventing workpieces from gliding. The automatic loading device comprises a bottom slot, a side plate, a shaft lever, a gear,a stress rod, a blocking part, an ascending part, an anti-sliding part, a middle hole, side parts, a blocking slot, a guide slot and a stress hole, wherein a main body is a rectangular internal hollow structure, and a bottom part is a rectangular plate-shaped structure; the two sides inside the main body are equipped with guide plates of rectangular structures; a baffle plate is arranged inside the main body; moving parts are mounted at the two sides of the bottom end inside the main body through connectors, and bottoms of bottom wheels are in contact with the bottom end of the main body; a trigger part is triggered, so that limiting on the side parts is relieved, and therefore, springs can support the ascending part to integrally drive the workpieces to ascend; and the top end of the trigger part is positioned inside a middle hole in the middle position of the ascending part, so that the trigger part can be pressed to move while the workpieces are placed, and therefore, the trigger part is pressed to trigger, and the moving parts are controlled to relieve limiting on the side parts.