A conventional broadband quarter-wave plate has not completely solved the
wavelength dependence and has different efficiencies of shifting the
phase by 90.degree. depending on the wavelengths, and therefore has a
problem that it cannot fulfill the strict specifications on the optical
characteristics which are demanded of a wave plate from a viewpoint of
the optical efficiency and the like in an optical pickup device
compatible with a plurality of different wavelengths. To provide a wave
plate which completely functions as a quarter-wave plate with respect to
a plurality of different wavelengths and an optical pickup using that
wave plate to solve the problem, the present invention provides a
laminated wave plate, wherein a wave plate with a phase difference
.alpha. and a wave plate with a phase difference .beta. with respect to
monochromatic light with a wavelength .lamda. are laminated in such a way
that directions of optical axes of said plates intersect each other, so
that the laminated wave plate, as a whole, functions as a quarter-wave
plate, and which is characterized in that a relationship between the
.alpha. and the .beta. satisfies the following formulas:
(3/2).times..pi..noteq..alpha.-2.times..pi..times.(m-1)
.pi..noteq..beta.-2.times..pi..times.(n-1), wherein: each of m and n is a
positive integer.