Abstract: A rod lens array 3, a line image sensor 4, and a line image sensor 5 are provided in such a manner that a distance A1 between a point A of an object surface and one end of a rod lens array 3 is the same as a distance A2 between the other end of the rod lens array 3 and a light-receiving surface (i.e., an image formation surface) of a first line image sensor 4, and a distance B1 between a point B of the object surface and one end of the rod lens array 3 is the same as a distance B2 between the other end of the rod lens array 3 and a light-receiving surface (i.e., an image formation surface) of a second line image sensor 5.

Abstract: An aligning tool having a plurality of grooves formed side by side is provided; gradient index rod lenses are placed in alignment within the grooves at an average spacing of 1 &mgr;m-5 &mgr;m; the gradient index rod lenses are fixed to form an integral unit as they maintain the aligned state; thereafter the end faces of each rod lens are polished.

Abstract: In an image forming apparatus, an object surface (14) is disposed facing one end face of a rod lens array (10), while an image surface (16) is disposed facing the other end face thereof. A lens working distance of the rod lens array on the object side is substantially equal to that on the image side. An actual object-image distance Tco is set between the conjugate length TC1 at which the average value MTFave of the MTF of the rod lens array in the lens array direction is maximized and the conjugate length TC2 at which the &Dgr;MTF(=(MTFmax−MTFmin)/MTFave) is minimized, and a shift quantity &Dgr;TC(=|TCo−TC1|) is set within 0 mm<&Dgr;TC<+02 mm for the conjugate length TC1 at which the MTFave is maximized.