A laser device integrated with a spot size converter is provided to lower a cross-section reflectance and to improve optical coupling efficiency by using a tapering structure. A laser device includes a semiconductor substrate(31), a first optical waveguide(32), a second optical waveguide(33), and metal contact layers(35,36). The first optical waveguide is formed in a ridge shape on the semiconductor substrate in order to be coupled with an optical fiber. The second optical waveguide includes a semiconductor laser region, an optical modulation region, and an optical mode conversion region and is laminated on the first optical waveguide. The metal contact layers are formed on the second optical waveguide. In the second optical waveguide, a spot size converter having an inverse mesa shape is integrated in a tapering shape within the optical mode conversion region.
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