To automatically measure printing deviation amounts by using a camera of a screen printer.

An opaque or translucent film 38 for trial printing is stuck to a top face of a circuit board 19 so that a board mask 33 is not hidden, the circuit board 19 is carried in at a lower part of a screen mask 26, a mask mark of a lower surface of the screen mask 26 and two imaging areas are picked up with a camera 34 to recognize a position of the mask mark and positions of mask openings 31 in the respective imaging areas. After this, after performing screen printing of printing patterns to the film 38 for trial printing on the circuit board 19, a printing pattern printed by the mask openings 31 in the imaging areas of the screen mask 26 printing patterns among the printing patterns on the film 38 for trial printing of the and the board mask 33 are picked up with the camera 34 to be recognized, and position deviation amounts between the positions of the mask openings 31 and the positions of the printing patterns are calculated as printing deviation amounts.