Patent ID: 7272100

Claim:
In an optical head apparatus, comprising: a laser beam-emitting element, a prism used for optical path synthesis or optical path separation of an incident laser beam emitted from said laser beam-emitting element, a collimating lens to convert said laser beam transmitted through said prism to parallel light flux, and an objective lens to condense parallel light flux emitted from said collimating lens on optical recording medium, being located on an optical path in the recited order; said prism being provided with a No. 1 prism structural member and a No. 2 prism structural member joined through a partially reflecting face slanted toward an optical axis of said laser beam emitted from said laser beam-emitting element; and said optical head apparatus having specified conditions designated for a value obtained from Δn·d, or for Δn, when length of said laser beam in an optical path direction in said prism, and absolute value of the difference in refractive index between said No. 1 prism structural member and said No. 2 prism structural member are respectively termed d, Δn, wherein the following equation is satisfied: 5>Δ n·d/λ within the effective pupil in said prism, when the wavelength of said laser beam is termed λ.