A hologram recording/reproducing device includes a recording/reproducing optical unit performing recording and reproducing operations on a hologram recording/reproducing medium. The optical unit includes a laser light source emitting laser light; a spatial-light modulator generating signal light and reference light from the laser light, the signal light and reference light having a common light path; a phase mask disposed near the modulator or in a conjugate plane of the modulator and transmitting at least the reference light; and an objective lens including a first lens portion and a second lens portion. The first lens portion is disposed at an inner peripheral portion of the objective lens and serves as a Fourier transformation lens focusing the signal light to a predetermined point. The second lens portion is disposed at an outer peripheral portion of the objective lens and has focuses continuously or discretely disposed in an optical-axis direction of the objective lens and at portions in the medium near the predetermined point.