An optical space communication method is for communication with a laser as a radiative source and with a light signal therefrom propagating in the atmosphere. In the method, the communication is performed under the following conditions. In case a transmission distance of optical space communication is between 100 m inclusive and 200 m, the laser is a laser with an oscillation wavelength L (nm) in a wavelength range of between 967 run inclusive and 1110 nm or in a wavelength range of between 1165 nm inclusive and 1315 nm, whereas in case the transmission distance is not less than 200 m, the laser is a laser with an oscillation wavelength L (run) in a wavelength range of between 986 nm inclusive and 1090 nm or in a wavelength range of between 1225 nm inclusive and 1295 nm. At any position in a transmission path between a transmitter exit and a receiver entrance, an irradiance is set to at most 6.47.multidot.10.sup.(L-700)/500 (W/m.sup.2) where the oscillation wavelength L (nm) of the laser is in a wavelength range of 950 nm to 1050 nm while to at most 32.3 (W/m.sup.2) where the oscillation wavelength L is in a wavelength range of 1050 nm to 1400 nm.