A mask tension welding device for welding a mask for thin film deposition on a mask frame, the mask tension welding device including a tension unit to pull the mask in one direction; a pressurizing unit to press the mask to the mask frame, the pressuring unit including an upper housing, a lower housing coupled to the upper housing, a window between the upper housing and the lower housing, a space in the lower housing into which a fluid is injectable, and an inlet and an outlet to provide a passage through which the fluid is injected and discharged; and a laser welding unit to weld the mask and the mask frame to each other.