An achromatic lens system is provided with a cemented resin lens having positive refractive power constructed by a resin lens L11 having positive refractive power cemented with a resin lens L12 having negative refractive power, and a close-contact multi-layer type diffractive optical element L11E, the diffractive optical element L11E being disposed to an image side of the cemented resin lens, the diffractive optical element L11E being constructed by cementing two diffractive element members DE11, DE12 each made of different optical materials with each other, and the cemented surface thereof being a diffractive optical surface Gf on which grooves of a diffraction grating are formed, there by being lightweight and easily manufactured, capable of excellently correcting chromatic aberration and spherical aberration at the same time.