A smaller and higher performance optical transmitter module is provided, which can improve the reliability and which can be manufactured at lower costs and allow for stable laser transmission of an optical semiconductor element. The optical transmitter module which has an optical semiconductor element, an optical fiber optically coupled to the optical semiconductor element, an inline optical isolator provided for the optical fiber, and a package case containing the optical semiconductor element and the optical fiber, includes a substrate member with one end of the optical fiber on the light incident side fixed thereon to be optically coupled to the optical semiconductor element, a thermoelectric cooler with the substrate member joined to the top surface thereof, and a pipe-like support member projecting from the side face of the package case for fixing the optical isolator.