To provide a high performance and bright triplet lens using a diffraction optical element by constituting it with a positive lens, a negative lens and the positive lens from an object side, providing at least a surface of diffraction surface and being satisfied with a specified condition.

This triplet lens is provided with a brightness diaphragm r8, and is constituted of respective positive, negative, positive lenses from the object side, and is provided with at least a surface of diffraction surface r3, and is satisfied with the condition by the expression I; 0.5<Σ(PDmax-PDmin)/PDmax)<2.5. In the expression I, PDmax, PDmin are made respectively a maximum value, a minimum value of power PD (y) of the diffraction surface at a height (y) from an optical axis in a valid system defined by the expression II, and Σ means that the sum of all surfaces is worked out. In the expression II, (n) is a diffractive index of a (d) line, rD1 (y) is an object side radius of curvature, rD2 (y) is an image side radius of curvature, and however, the rD1 (y), rD2 (y) are made a radius of paraxial curvature when an aspherical effect doesn't exist, and are made the radius of curvature defined by the expression III when exists. In the expression III, (y) is the height from the optical axis, the f (y) is an aspherical definitive relation.