An information recording and reproducing apparatus including a recording medium that includes at least a substrate, a reflection layer disposed on the substrate, and a recording layer disposed so as to interpose the reflection layer between the substrate and the recording layer, and a near-field optical head, disposed close to the recording medium, for irradiating the recording medium with near-field light to effect recording and reproduction of information. The near-field optical head includes a light-blocking metal film which includes a dielectric base material provided with a small opening and which is disposed opposite to the reflection layer disposed on the substrate, so that the light-blocking metal film and the reflection layer constitute an optical resonator to increase intensity of the near-field light. The optical resonator satisfies the following resonance condition: 4.pi.L/.lamda.+.phi.1+.phi.2=2m.pi., wherein L represents an optical path between a bottom surface, of the near-field optical head, at which the light-blocking metal film is disposed; .lamda. represents a wavelength in a vacuum of a light source used in the near-field optical head; .phi.1 represents a phase shift due to reflection by the light-blocking metal film; .phi.2 represents a phase shift due to reflection by the reflection layer; and m represents a positive integer.