A zoom lens has, on the most object side, a first lens unit that has a prism with a reflecting surface for folding the path of rays, that has a negative refractive power in its entirety and that is fixed in a magnification change, and an aperture stop that is fixedly positioned in reference to the image pickup surface. The ray-entering surface of the prism has an aspherical surface concave toward the object side that exerts a weaker power for divergence at a position thereon farther from the optical axis. Whereby, a zoom lens with high optical specification performance and extremely thin size in depth direction is provided.