PURPOSE: To provide an optical space transmitter in which it is prevented that a transmission unit makes optical alignment of its laser beam in mistake to an external light or the like by eliminating a noise of a light receiving signal.

CONSTITUTION: This transmitter is provided with a transmission unit outputting a laser beam modulated by a prescribed information signal and with a reception unit receiving the laser beam and demodulating the received beam, the reception unit outputs a detection light for detecting a radiation position deviation of the laser beam for a prescribed period, and the transmission unit is provided with plural light receiving elements 91c, 91d receiving the detection light, timing detection circuits 22,25-28 taking the sum of light receiving signals b, c of the light receiving elements to detect an output timing of the detected light, and a sample-and-hold circuit 36 that holds a signal (k) being a difference between two kinds of signals i, j being differences of the light receiving signals b, c of the light receiving elements 91c, 91d taken for a prescribed time interval based on a timing signal (h) from a timing detection circuit.