An optical space transmission module reduces an upper limit of light output based on a safety standard of a laser, reduces light returned to a laser, and is made smaller in size. The optical space transmission module includes a light emitting section which outputs a transmission light, a base section including a reflection section which reflects the transmission light, and a reflection type diffusion section which reflects and converts into a diffused light the reflected light which has been reflected by the reflection section. The reflection section has a function to increase a beam diameter of the transmission light after reflection.