PURPOSE: To cause the title device to cope with a laser chip assembled by a junction-down system while occurrence of cross talks is prevented by forming light condensing grating couplers which lead monitor light to waveguides and, at the same time, light receiving elements at the positions to which each monitor is condensed.

CONSTITUTION: Waveguides which propagate monitor light in the monitor light projecting direction on a substrate are provided and light condensing grating couplers 7 which lead the monitor light to the waveguides are formed on the waveguides. At the same time, light receiving elements 4 are formed in such a state where the elements 4 are respectively brought into contact with the waveguides at the positions to which each monitor light refracted by each grating coupler is condensed. Therefore, the junction-down system can be coped with this device and, as a result, deterioration of the performance of the light receiving elements 4 can be prevented because heat is easily diffused into the substrate. Thus the reliability of the light emitting device can be improved and occurrence of cross talks between the laser light and adjacent monitor light can be prevented.