To properly maintain a back focus without using an spherical lens, while realizing compact type, by inseating a negative lens having a prescribed refracting power at the pre-stage of a front joint lens, applying a gauss type lens constitution, regarding a large-aperture lens for photographing at low illuminance.

This lens is made of a double convex lens L1, a positive meniscus lens L2 with the concave surface directed toward an object, a negative lens L3 with the concave surface of strong curvature directed toward an image, a positive meniscus lens L4 (jointed to lens L5) with the convex surface directed toward the object, a negative meniscus lens L5 with the concave surface directed toward the image, a double concave lens L6 (jointed to lens L7) with the surface of strong curvature directed toward the object, double convex lenses L7 and L8 with the surfaces of strong curvature directed toward the image, and a positive meniscus lens L9 with the convex surface directed toward the object, arrayed respectively in order from the object. Also, constitution is so made that a relationship of 0.35<f/f3<0.56 is satisfied, where the focal distance of a while system is (f) and the focal distance of the third lens is f3.