The present invention provides a light-transmitting module capable of emitting light in stable under a predetermined temperature, especially the light-transmitting module applicable to a condition when the predetermined temperature is lower than ambient temperatures. The light-transmitting module of the present invention includes a light-emitting module, which encloses the laser diode and the Peltier device therein, a substrate electrically connected to the light-emitting module, and a heater. The heater is able to heat the package of the light-emitting module when the predetermined temperature of the laser diode is higher than the ambient temperature, thereby preventing the temperature of the package from lowering the dew-point and droplets from being generated on the substrate. The optical output from the light-transmitting module can be stabled.