A stamp-face platemaking device transports a medium holder inserted into a plate insertion portion to a printing unit. The medium holder holds a stamp face material in a plate-like member, and has a predetermined pattern in a side end portion thereof. An optical sensor detects the top end portion of the medium holder on a sensor scanning line in the inserting direction, and the pattern start point and the pattern end point of the predetermined pattern. At least one of the horizontal and vertical sizes of the stamp face material is set based on the positions of two of the detected end portions. When the pattern end point is detected, platemaking with the stamp face material is started.