A screen printer in which a photoelectric sensor and squeegees are fixed to a slider, when outward movement printing in which solder on a screen is rolled by an outward movement of the right squeegee is completed, the right squeegee is separated from a state of contacting a right end of a solder roll and a squeegee position pl at that time is input, and, subsequently, the slider is returned until the photoelectric sensor detects a left end of the solder roll and a squeegee position p2 at this time is input. An amount (a solder roll width) of solder remaining on the screen is calculated by subtracting a movement amount from the squeegee position p1 to the squeegee position p2 from a distance from the right squeegee to an optical axis position of the photoelectric sensor on the screen.