A light source module includes a light source which comprises a light emitting element, a stem configured to support the light emitting element, and a terminal having one end electrically connected to the light emitting element, a wiring board to which the other end of the terminal is electrically connected and which is configured to electrically connect the terminal to an external power supply terminal, and a thermal diffusion member which is disposed between the stem and the wiring board and is thermally connected to the light emitting element.