An imaging lens includes a first lens having positive refractive power; a second lens; a third lens; a fourth lens; and a fifth lens having negative refractive power, arranged in this order from an object side to an image plane side. A drive section is built into a tray which can be extracted from and retracted into an external chassis and moves a disk-shaped recording medium between the ejecting position and the recording-reproducing position. The lens array unit is secured in the recess of the housing by engaging the right projection with the right groove and engaging the left projection with the left groove.