Disclosed is an optical transmission module in which effects of conductive heat from sides of a metal case upon a thermistor are reduced, thereby allowing steady optical beam wavelengths to be obtained over a wide range of temperatures, regardless of the temperature of the usage environment. Specifically, the optical transmission module includes Peltier elements disposed inside a metal case, a metal base disposed upon the Peltier elements, a laser diode substrate disposed upon the metal base, a laser diode disposed upon the laser diode substrate, a thermistor substrate disposed upon the metal base, a thermistor disposed upon the thermistor substrate, and a thermally conductive member, disposed in the vicinity of the thermistor, that has a height greater than the height of the thermistor.