PURPOSE: To facilitate the work for optical axis alignment at the time of assembling a microlens into an optical device by fitting a microoptical element into a specific through-hole and fixing this element.

CONSTITUTION: A plane plate member 1, which is a holder, is constituted by forming a light shielding film 15 on one surface of a transparent plane plate 120, such as quartz plate or glass plate, forming a metallized film 17 on the other surface and boring the plate member with the through-hole 2 having a sectional shape uniform in the through direction. In such a case, the microoptical element 10 to be held is, for example, a transparent spherical microbody and has a diameter slightly larger than the diameter of the through- hole 2 of the plane plate member 1. The element is fitted into the through hale 2 to be held. The 'microoptical element unit' is constituted if the microoptical element 10 is fixed to the plane plate member 1 by means such as adhering in this state. The microlens is assembled into the optical device by the holder maintaining the unequivocal relation with its optical axis in such a manner.