Optical pickup device capable of detecting stable error signal

An optical pickup device comprising:

• a first light source for generating and emitting light;
• first light path changing means for changing a traveling path of incident light;
• focusing means for focusing the incident light from the light path changing means onto a recording medium;
• and
• a first signal detection unit having a hologram element for diffracting incident light after being reflected from the recording medium, a photodetector for receiving the light diffracted by the hologram element and converting the same into an electrical signal and a signal operation unit for generating a focus error signal and/or a track error signal from a detection signal of the photodetector, the signal detection unit for receiving the light reflected from the recording medium and then passed through the focusing means and the first light path changing means, wherein the hologram element includes first and second pattern portions arranged to be spaced apart a predetermined distance from each other, for diffracting and focusing incident light, and third and fourth pattern portions arranged close to the first and second pattern portions, respectively, for diffracting incident light in different directions, the first and second pattern portions being provided such that ±1st-order diffracted beams are focused on first and second focuses, respectively, and wherein the photodetector includes first and second light receiving units positioned between the first and second focuses in an on-focus state, for receiving the light diffracted and focused by the first and second pattern portions, and third and fourth light receiving units for receiving the light diffracted by the third and fourth pattern portions.