Refracting objective optical system and optical recording/reproducing device using the same

A refracting objective optical system comprising:

• an aspherical lens in which an entrance surface is a continuous aspheric surface of convex shape and an exit surface is a flat surface;
• and
• a transparent flat plate joined to the flat surface of the aspherical lens, where the ray entering the aspheric surface of the aspherical lens is refracted at the aspheric surface, transmitted through the flat surface or the joint surface, and condensed near the exit surface of the transparent flat plate,
• wherein the transparent flat plate includes a microscopic structure for generating a near field light smaller than a light condensing spot near the light condensing point of the exit surface and satisfies the following condition
• 0.01<tP/tL<1.0,
• where the thickness of the transparent flat plate is tP and the thickness of aspherical lens is tL.