PURPOSE: To improve the S/N of a detecting means, and reduce its erroneous detection by using a transparent transfer sheet carrying belt and a reflecting member to increase the light quantity returned to an optical sensor when no resist mark is present on the transfer sheet carrying belt.

CONSTITUTION: To read each resist mark, a lens 15 and a light emitting and receiving part 17 for emitting an infrared ray to be absorbed by each resist mark are provided. In the place where no resist mark is recorded, the light emitted from the light emitting and receiving part 17 is transmitted by a transfer sheet carrying belt 1, reflected by a reflecting member 18, again transmitted by the transfer sheet carrying belt 1, and detected by the light emitting and receiving part 17, while, in the place where the resist mark is recorded, the light emitted from the light emitting and receiving part 17 is absorbed by the resist mark. Thus, compared with a conventional method for recording the resist mark on a transfer sheet, the reflected light from the transfer sheet in the resist mark recorded place is eliminated.