A hologram recording/reproducing device records information onto a medium by a light beam emitted from a laser light source and passing through a forward path, the forward path having optical components in an area extending from the laser light source to the medium, and reproduces the recorded information by the light beam passing through a backward path, the backward path having optical components in an area extending from the medium to an array light detector. The device includes a spatial-light modulator and a first objective lens disposed in the forward path, and a second objective lens and a polarization-dependent diffraction element disposed in the backward path. The modulator generates signal light and reference light from the light beam emitted from the laser light source, the signal light and the reference light being spatially divided from each other and having a common light path. The first objective lens focuses the signal light and the reference light from the modulator onto the medium. The second objective lens forms a hologram image on the light detector based on reproduction light from the medium. The diffraction element is disposed in a hologram real-image plane and diffracts the reference light incident upon the light detector from the second objective lens.