PURPOSE: To generate clock signals at regular intervals at high speed with high accuracy at low cost.

CONSTITUTION: An artifact 2 having the type of a concentric annular diffraction grating to the center of a disk 6 is installed onto the disk 6 housed in a disk housing device. The artifact 2 is irradiated with electromagnetic radiation under the state, in which the disk 6 is rotated, and the electromagnetic radiation is diffracted by the artifact 2. The diffracted electromagnetic radiation is directed towards a structuralized clock detector housed in a module 10, electromagnetic radiation diffracted by the structuralized clock detector is received and the output signal is processed, and a fixed number of clock signals at regular intervals to the revolution of the disk 6 are generated.