The semiconductor laser device comprises a laser part, a waveguide for propagating laser light emitted by the laser part, and a photodetector for detecting the laser light which are formed on the same semiconductor substrate. The photodetector includes a p-type contact layer which is formed above the side of the waveguide on the side opposite to the semiconductor substrate and is connected to an anode electrode, an n-type contact layer connected to a cathode electrode, and an undoped layer formed between the p-type contact layer and the n-type contact layer. The undoped layer and the n-type contact layer in the photodetector include a main light receiving part disposed above the waveguide so as to encompass the waveguide, and an enlarged part disposed so as not to encompass the waveguide while connected to the main light receiving part.