PURPOSE: To facilitate the new construction of a recording and reproducing system for high density by setting a prescribed pitch, width, depth inclination and opening number to be prescribed values to a transparent substrate with a large thickness.

CONSTITUTION: A laser beam with a wavelength is converged to the optical recording medium of the group of a track pitch P, width W, depth D, inclination βon the transparent substrate with a refractive index (n) by an objective lens with the opening number η with a beam radius W0 (W0/λ=0.48/η) so that light intensity at a focal plane is 1/e2 of a center and a reflected light beam is converged by the objective lens. Then, the reflected light beam is converged by the objective lens and the track pitch P, width W, depth D, inclination 4 and opening number η so that a push-signal to be the difference of the minimum value of the D, P, D, R of a formula described here-under is 0.4-0.7 are set by a bi-sected photodetector. In the formula, (u) is a scalar function representing the Z component of magnetic field with electric field in an area Q.