An optical pickup for reading information written on an optical disk is equipped with a laser diode having a front facet which emits light, a parallel light ray portion which collimates the emitted light from the laser diode, means for focusing collimated output light onto the optical disk, means for receiving reflected light from the optical disk, and an optical element having an index of refraction of 1 or higher for adjusting the length of the optical path between the front facet of the laser diode and the optical disk, wherein the optical element is inserted in the parallel light ray portion when the optical path length lies within the range of the expression"(n-0.5.+-.0.25).times.the effective cavity length of the laser diode" (where n is a positive integer) in order to reduce the noise in the emitted light of the laser diode.