Provided is an optical space transmitter and an optical space transmission method, for wavelength-multiplexed light, capable of obtaining a wavelength-multiplexed signal by multiplexing optical signals having a plurality of wavelengths with a simple configuration and without requiring highly precise adjustment for optical axes and enhancing safety for a human body, including, e.g., the eyes. The transmitter has a configuration for which light sources (101a, 101b) for outputting signal lights having wavelengths different from each other are arranged so as to irradiate an approximately identical portion of a diffusion plate (104), a diffuse light outputted from the diffusion plate (104) is converted, by a radiation lens (105), into a light traveling with an angle suitable for transmission in a free space, and the converted light is passed out to the free space. Accordingly, without requiring a highly precise adjustment for optical axes, it is possible to realize a wavelength multiplexing optical space transmitter operable to multiplex optical signals having wavelengths different from each other based on a coincided optical axis, and to reduce risk of eye injury.