PURPOSE: To provide the resonator which has high shape accuracy, is improved in coupling of resonance light and has the specified shape of an optical surface in spite of mass production by forming the surface shape of at least a part of an end face to be formed as an optical surface by a photoapplication utilizing the characteristics of light.

CONSTITUTION: The flat end surface of a three-dimensional block material 1 of a nonlinear optical material is provided with a resist film 3 of a negative type and the surface of this film is irradiated with a laser beam 4 converged to a small beam diameter, by which the projecting body derived from the irradiated region 3A of the resist film 3 is formed on the surface of the block material 1. The etching part of the block material 1 is simultaneously etched and the projecting surface shape complying with the surface shape of the original projecting body 2 remains on the end face of the block material 1 when the projecting body 2 which is a residue of the resist film 3 is removed by etching. This projecting surface shape is the shape complying with the cumulative intensity distribution of the irradiation point irradiated with the laser beam 4. Mainly, the central part on such projecting surface shape is utilized as the optical surface of the monolithic ring resonator.