Objective lens and optical device

In an objective lens having aspheric surfaces at both surfaces, used in an optical system in which light having a first wavelength is converged to the data recording surface of a first optical disk and reflection light from the data recording surface of the first optical disk is received by a light receiving element in recording or reading the first optical disk, and light having a second wavelength which is different from the first wavelength is converged to the data recording surface of a second optical disk and reflection light from the data recording surface of the second optical disk is received by the light receiving element in recording or reading the second optical disk, the objective lens being characterized in that:

• a phase shifter provided with annular step portions W having a center coincident with an optical axis of the lens is formed in a single or both surfaces of the objective lens, wherein the phase shifter has function to produce a phase difference for reducing the aberration resulted in recording or reading the first optical disk with respect to the light having the first wavelength, and has function to produce a phase difference for reducing the aberration resulted in recording or reading the second optical disk with respect to the light having the second wavelength.