A screen printing apparatus including two screen printers, each including a substrate introduction portion by which a substrate is introduced from an upstream side of a component mounting line, a printing portion which performs a screen printing to the introduced substrate, a substrate discharge portion by which the substrate is discharged to a downstream side, and a substrate moving stage which receives the substrate to position the substrate with respect to the printing portion and to move the substrate to the substrate discharge portion. The two substrate introduction portions, the two printing portions, and the two substrate discharge portions are arranged symmetrically to each other with respect to a perpendicular symmetrical plane extending in a transportation direction of the substrate in the component mounting line, respectively. Each printing portion is provided at a position further from the perpendicular symmetrical plane than the substrate discharge portion.