A zoom lens having a variable image magnification, for introducing object light from an object side toward a light receiving surface on an optical axis, is provided. An objective lens system has a positive refractive power, and includes a prism for reflecting the object light being incident to guide the object light on the optical axis, and an aperture stop control device for passing the object light, the objective lens system forming an intermediate image by focusing the object light nearer to the object side than the light receiving surface. A relay lens system has a positive refractive power, includes plural lens groups movable on the optical axis, is disposed behind the objective lens system as viewed from the object side, for zooming and refocusing the intermediate image. Also, a distance between the plural lens groups is shortest in zoom setting in the telephoto end position.