Provided are a lens, a stem, an LD chip to emit laser light with a beam center directed along a mounting surface of the stem, and a PD chip having a reflective surface formed with a dielectric multilayer film on its surface, reflecting the laser light emitted from the LD chip toward the lens, and measuring an amount of the laser light, wherein the LD chip is provided with a waveguide portion having a tip portion that is formed on a side of a front end face and has a width of 0.5 to 0.7 μm, and having a tapered portion that is connected to the tip portion and becomes narrower toward the tip portion at a gradient of 0.018 to 0.033.