An achromatic lens system comprising: a close-contact multi-layer type diffractive optical element (L11E, L21E, L31E); a cemented resin lens having positive refractive power constructed by a resin lens having positive refractive power cemented with a resin lens having negative refractive power; the close-contact multi-layer type diffractive optical element being provided to an image side of the cemented resin lens and being constructed by cementing two diffractive element members (DE11, DE12) made of different optical materials with each other, and the cemented surface thereof being a diffractive optical surface on which grooves of a diffraction grating are formed; the two diffractive element members (DE11, DE12) composing the diffractive optical element being different to each other, and at least one of them, being made of an ultraviolet curing resin material, and the following conditional expression being satisfied: 0.2 ≤ | R / f | ≤ 1.8 where R donates a radius of curvature of the cemented surface of the cemented resin lens, and f denotes a focal length of the achromatic lens system, characterised by that the following conditional expressions are satisfied: nd 1 ≤ 1.54 0.0145 ≤ nF 1 − nC 1 1.55 ≤ nd 2 nF 2 − nC 2 ≤ 0.013 where nd1 denotes a refractive index of a material of the diffractive element member having a lower refractive index and a smaller Abbe number among the two diffractive element members (DE11, DE12) of the diffractive optical element at d-line (wavelength λ=587.562 nm), nF1 denotes a refractive index of a material of the diffractive element member having a lower refractive index and a smaller Abbe number among the two diffractive element members of the diffractive optical element at F-line (wavelength λ=486.133 nm), nC1 denotes a refractive index of a material of the diffractive element member having a lower refractive index and a smaller Abbe number among the two diffractive element members of the diffractive optical element at C-line (wavelength λ=656.273 nm), nd2 denotes a refractive index of a material of the diffractive element member having a higher refractive index and a larger Abbe number among the two diffractive element members of the diffractive optical element at d-line (wavelength λ=587.562 nm), nF2 denotes a refractive index of a material of the diffractive element member having a higher refractive index and a larger Abbe number among the two diffractive element members of the diffractive optical element at F-line (wavelength λ=486.133 nm), and nC2 denotes a refractive index of a material of the diffractive element member having a higher refractive index and a larger Abbe number among the two diffractive element members of the diffractive optical element at C-line (wavelength λ=656.273 nm). a close-contact multi-layer type diffractive optical element (L11E, L21E, L31E); a cemented resin lens having positive refractive power constructed by a resin lens having positive refractive power cemented with a resin lens having negative refractive power; the close-contact multi-layer type diffractive optical element being provided to an image side of the cemented resin lens and being constructed by cementing two diffractive element members (DE11, DE12) made of different optical materials with each other, and the cemented surface thereof being a diffractive optical surface on which grooves of a diffraction grating are formed; the two diffractive element members (DE11, DE12) composing the diffractive optical element being different to each other, and at least one of them, being made of an ultraviolet curing resin material, and the following conditional expression being satisfied: 0.2 ≤ | R / f | ≤ 1.8 where R donates a radius of curvature of the cemented surface of the cemented resin lens, and f denotes a focal length of the achromatic lens system, characterised by that the following conditional expressions are satisfied: nd 1 ≤ 1.54 0.0145 ≤ nF 1 − nC 1 1.55 ≤ nd 2 nF 2 − nC 2 ≤ 0.013 where nd1 denotes a refractive index of a material of the diffractive element member having a lower refractive index and a smaller Abbe number among the two diffractive element members (DE11, DE12) of the diffractive optical element at d-line (wavelength λ=587.562 nm), nF1 denotes a refractive index of a material of the diffractive element member having a lower refractive index and a smaller Abbe number among the two diffractive element members of the diffractive optical element at F-line (wavelength λ=486.133 nm), nC1 denotes a refractive index of a material of the diffractive element member having a lower refractive index and a smaller Abbe number among the two diffractive element members of the diffractive optical element at C-line (wavelength λ=656.273 nm), nd2 denotes a refractive index of a material of the diffractive element member having a higher refractive index and a larger Abbe number among the two diffractive element members of the diffractive optical element at d-line (wavelength λ=587.562 nm), nF2 denotes a refractive index of a material of the diffractive element member having a higher refractive index and a larger Abbe number among the two diffractive element members of the diffractive optical element at F-line (wavelength λ=486.133 nm), and nC2 denotes a refractive index of a material of the diffractive element member having a higher refractive index and a larger Abbe number among the two diffractive element members of the diffractive optical element at C-line (wavelength λ=656.273 nm).