Provided is a retrofocus type optical system including a lens or a layer made of a material satisfying the following conditions of the Abbe constant .nu.d and partial dispersion ratios .theta.gd and .theta.gF, .nu.d<30, .theta.gd<-3.333.times.10.sup.-3.nu.d+1.40, .theta.gF<-2.615-10.sup.-3.nu.d+0.67. In the case that this layer is disposed on the front side of the aperture stop, the layer is designed to have a positive refractive power, and in the case that the layer is disposed on the rear side of the aperture stop, the layer is designed to have a negative refractive index.