A zoom lens includes a first lens unit fixed when the magnification of the zoom lens is changed and at least two positive lens units arranged on the image side of the first lens unit so that relative spacings between individual lens units are varied when the magnification is changed. The first lens unit has a prism containing a reflecting surface at the most object-side position, the entrance surface of the prism is configured as a concave surface directed toward the object side, and the concave surface is an aspherical surface that divergence is impaired progressively in separating from the optical axis.