Abstract: A cutting plotter equipped with a device for reading register marks for seal cutting capable of accurately reading the register marks printed on a seal material. The cutting plotter includes a head provided thereon with a light emitting element for emitting a predetermined amount of light toward a surface of the seal material and a light receiving element for detecting the amount of light reflected from the surface of the seal material. A difference between the amounts of reflected light detected by the light receiving element is calculated by a first calculation unit and then stored in a storage unit. A relative difference between the difference in the amounts of reflected light stored in the storage unit and a difference between the amounts of reflected light calculated by the first calculation unit is calculated by a second calculation unit.