An optical information recording/reproducing apparatus includes a spatial light modulator that converts an irradiation beam emitted from a light source to a single information beam that carries information; an optical system that causes the single information beam to be collected on an optical-information recording medium including an information recording layer capable of recording the information as hologram by using interference fringes produced due to interference between the single information beam and a plurality of reference beams, and causes each of the reference beams to be irradiated to the optical-information recording medium from mutually different directions so as to intersect with the single information beam in the information recording layer; and a controller that controls to cause the light source to emit the irradiation beam and performs angular multiplexing recording of the information in the information recording layer while controlling to drive either one of the optical-information recording medium and the optical system.