Screw fastening machine

The utility model discloses a screw fastening machine which is mainly used for automatically assembling screws on products on a production line. The screw fastening machine comprises an air cylinder (4), wherein the air cylinder (4) drives a screw fastening mechanism to move up and down. The screw fastening machine is characterized in that the air cylinder (4) is a double-piston-rod air cylinder, air cylinder rods at two ends of the air cylinder (4) are connected with a fixing base (1) and a fixing board (3) respectively, the screw fastening mechanism is connected with a cylinder barrel of the air cylinder (4), and two end covers of the air cylinder (4) are respectively provided with a sliding block (2) which is matched with the fixing board (3) in a sliding mode. The screw fastening machine is simple in structure, reliable in work, capable of greatly reducing construction cost of the equipment and improving assembling quality of the products.