A spatial optical transmitter comprising: a light source for outputting a light of a single wavelength; a modulation unit for modulating the light output from the light source in accordance with a signal to be transmitted to generate a modulated optical signal of a single polarization; a transmission-side dividing unit for dividing the optical signal generated by the modulation unit into two; a polarization rotating unit (13a, 13b) for rotating polarizations of the optical signals divided by the transmission-side dividing unit to generate optical signals of two orthogonal polarizations; two transmission-side optical systems (14a, 14b, 15a, 15b) for transmitting the optical signals of two polarizations generated by the polarization rotating unit (13a, 13b) to space, individually; and a direction control mirror (57a to 57c) for controlling direction of the optical signal output from the transmission-side optical system; characterized in that the optical signals of two polarizations generated by the polarization rotating unit (13a, 13b) are a right-handed circularly polarized light and a left-handed circularly polarized light; and the spatial optical transmitter further comprises: a transmission-side beam splitter (59a to 59c) for dividing the optical signal whose direction is controlled by the direction control mirror (57a to 57c) into a first optical signal and a second optical signal and transmitting the first optical signal to space; and a direction control unit for detecting a directional deviation of the second optical signal and controlling the direction control mirror (57a to 57c) so that the detected directional deviation is compensated. a light source for outputting a light of a single wavelength; a modulation unit for modulating the light output from the light source in accordance with a signal to be transmitted to generate a modulated optical signal of a single polarization; a transmission-side dividing unit for dividing the optical signal generated by the modulation unit into two; a polarization rotating unit (13a, 13b) for rotating polarizations of the optical signals divided by the transmission-side dividing unit to generate optical signals of two orthogonal polarizations; two transmission-side optical systems (14a, 14b, 15a, 15b) for transmitting the optical signals of two polarizations generated by the polarization rotating unit (13a, 13b) to space, individually; and a direction control mirror (57a to 57c) for controlling direction of the optical signal output from the transmission-side optical system; characterized in that the optical signals of two polarizations generated by the polarization rotating unit (13a, 13b) are a right-handed circularly polarized light and a left-handed circularly polarized light; and the spatial optical transmitter further comprises: a transmission-side beam splitter (59a to 59c) for dividing the optical signal whose direction is controlled by the direction control mirror (57a to 57c) into a first optical signal and a second optical signal and transmitting the first optical signal to space; and a direction control unit for detecting a directional deviation of the second optical signal and controlling the direction control mirror (57a to 57c) so that the detected directional deviation is compensated. a transmission-side beam splitter (59a to 59c) for dividing the optical signal whose direction is controlled by the direction control mirror (57a to 57c) into a first optical signal and a second optical signal and transmitting the first optical signal to space; and a direction control unit for detecting a directional deviation of the second optical signal and controlling the direction control mirror (57a to 57c) so that the detected directional deviation is compensated.