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. The transmitter has a configuration for which light sources for outputting signal lights having wavelengths different from each other are arranged so as to irradiate an approximately identical portion of a diffusion plate, a diffuse light outputted from the diffusion plate is converted, by a radiation lens, 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.