PURPOSE: To miniaturize an optical pickup device while maintaining the satisfactory sensitivity for detection of a focus error, etc., by attaining such a constitution where a laser beam reflected and sent back from an optical disk has its optical axis at an acute angle to the optical axis of a laser beam traveling its going route.

CONSTITUTION: A reflecting surface 12a of a beam splitter 12 is set at a sloping angle θ. Thus a laser beam reflected and sent back from the signal recording surface of an optical disk 15 is reflected so that its optical axis has a ≤90° acute angle to the optical axis of a laser beam traveling its going route to be made incident on the disk 15 from a semiconductor laser 11. The sent-back laser beam separated and reflected by the splitter 12 travels in an acute direction to the optical axis of the laser beam made incident on the disk 15. While a radiating surface 12b through which are sent-back laser beam reflected by the surface 12a is radiated from the splitter 12 is set vertical to the optical axis of the sent-back laser beam.