A light-converging optical system has an objective lens arranged at a position to be opposite to an optical information recording medium and including at least one plastic lens, and an aberration correcting element provided on an optical path between the light source and the objective lens and structured by two groups of a positive lens and a negative lens both being a plastic lens. The filling material stabilizes a discharge of the luminescent material. The crystal structure of the piezoelectric thin film is a mixture of a perovskite columnar crystal region having an ionic defect in which a portion of the constitutive elements of an oxygen ion, a titanium ion, and a zirconium ion is missing and a perovskite columnar crystal region of stoichiometric composition having no ionic defect. In an alternative form a barrel-shaped, molded plastic spacer is added.