To control a wavelength with a sufficient variable wavelength width according to a simple structure upon gas detection by a TDLAS.

A semiconductor laser device 1 for use in wavelength variable semiconductor laser absorption spectroscopic process is manufactured by laminating a semiconductor substrate 10, an active layer 12, and a clad layer 13 between a pair of electrodes 17 and 18. An optical waveguide consists of an active region, and a phase adjusting region and a DBR region both contiguous to the active region. A heating means 20 is provided on the upper surface of the clad layer 13 via an insulating layer 19 to heat the whole or part of at least phase adjusting region. This heating means 20 and the pair of electrodes 17, 18 are supplied with electric power from a single power supply 2.