To obtain a lens for reading an image whose angle of view is wide, whose cost is low and by which the excellent quality of a read image is obtained and which is bright by constituting the lens of four lenses, making one surface of at least either a 1st lens or a 3rd lens aspherical and arranging a diaphragm between a 2nd lens and the 3rd lens.

This lens is constituted by arraying a 1st positive lens L1 whose convex surface faces to an object side, a 2nd lens L2 consisting of a biconcave lens, a 3rd lens L3 consisting of a biconvex lens, and a 4th lens L4 consisting of a negative meniscus lens whose convex surface faces to an image-formation surface in order from the object side. One surface of at least either the 1st lens L1 or the 2nd lens L2 is aspherical. A diaphragm (i) is disposed between the 2nd lens L2 and the 3rd lens L3 and luminous flux made incident on along an optical axis X from the object side is formed into an image at an image- formation position P. A pair of 1st and 2nd lenses L1 and L2 and a pair of 3rd and 4th lenses L3 and L4 are formed of a pair of positive and negative lenses, respectively, so that aberration is efficiently compensated.