PURPOSE: To judge whether received transmission density is within a transmission density range established according to an appropriate ink quantity or not by a method wherein the transmission density is measured by receiving laser light having transmitted a light diffused transparent ink part of a transfer foil with a photomultiplier after emitting the laser light from one side of the transfer foil.

CONSTITUTION: A transfer foil 1 on a base sheet 2 of which a light diffused transparent ink part 3 of a specific pattern is printed passes between a light source 10 and a photomultiplier 11 in a printing press 5. A specific laser light is emitted from the light source 10 toward the photomultiplier 11. Then, this laser light passes an irradiated position of the light diffused transparent part 3. By receiving the laser light having transmitted the light diffused transparent ink part 3 with the photomultiplier 11, transmission density is measured. In the case where a microcomputer 15 judges that the measured transmission density is not within an established transmission density range, processes such as that it is make known to an operator with a warning lamp, a warning buzzer, etc., that the printing press is stopped, or that a mark or the like are attached to a defect position of the transfer foil are performed.