Abstract: A screen printing machine and its locking device are disclosed. The screen printing device comprises a printing frame for holding printing stocks, a screen frame for supporting a screen and a squeegee; and at least one locking device including a first electromagnetic member mounted on one of the printing frame and the screen frame and connected to a power source and an attracted member mounted on the other one of the printing frame and the screen frame. When the screen frame is closed to the printing frame, the power source supplies power to the first electromagnetic member to enable the first electromagnetic member to attract the attracted member; when the printing is finished, the power source is turned off which makes the attraction of the first electromagnetic member to the attracted member disappear, and the printing frame and the screen frame are unlocked.