A light emitting array including at least a plurality of light emitting elements, each of which is provided thereon with a microlens in one-to-one correspondence. Light emitting portions of the light emitting element are provided having the shape of a rectangle and formed so as to satisfy the relational expression, Lmin.ltoreq.D.ltoreq.P, where Lmin is the length of the shorter side of the rectangle, P an alignment pitch of the light emitting elements, and D the diameter of microlens. In addition, light emitting elements are formed in line on a transparent thin film layer to satisfy the relationship, T1.ltoreq.2D2, where T1 is the thickness of the transparent thin film layer and D2 the diameter of each microlens. The light emitting array may suitably be included in the light source unit which is then incorporated into image forming apparatuses for forming mono-color or multiple-color images.