Provided is a waveguide photodetector including: a first clad layer disposed on a substrate; a core layer disposed on the first clad layer and for absorbing predetermined light; a second clad layer disposed on the core layer; and at least one subsidiary layer inserted in the first clad layer and the second clad layer. In this structure, the photodetector has about the same spot size as that of an optical fiber or planar lightwave circuit (PLC), so that incident light can be absorbed without loss, and the photodetector can more efficiently combine with the optical fiber or PLC and operate even at high power.