a light source emitting a light beam;

an objective lens focusing the light beam onto an information recording medium;

a light detection part receiving the light beam reflected from the information recording medium; and

a light blocking part selectively blocking a part of the light beam located outside a fixed radial distance from the optical axis, and selectively blocking a part of the light beam located inside the fixed radial distance from the optical axis, the light blocking part provided in an optical path of the light beam between the information recording medium and the light detection part and centered on an optical axis,

wherein said light blocking part comprises:

a turning part selectively turning a plane of polarization of the part of the light beam; and

a transmission part selectively blocking the part of the light beam based on a direction of polarization of the part of the light beam, the light beam being incident on said transmission part after being emitted from said turning part, and

wherein said optical pickup unit further comprises a control part generating an aberration signal by comparing a first signal generated based on a first part of the light beam passing through a first region of said light blocking part and a second signal generated based on a second part of the light beam passing through a second region of said light blocking part, the first region of said light blocking part being provided internal to the second region thereof.