PURPOSE: To provide a light signal transmitter capable of inputting a high- intensity light signal to an optical fiber and executing fiber transmission without receiving the influence of SBS in external modulation.

CONSTITUTION: This light signal transmitter is constituted by cascade connecting a semiconductor laser beam source 7 or a fixed luminous intensity light source, a first external modulator 9 and a second external modulator 8 with transmission paths and transmits output light to the optical fiber transmission path 4. The signal to be transmitted is impressed to the first external modulator 9 to modulate the intensity of the input light to the first external modulator 9. The implantation current to the semiconductor laser beam source 7 or the output light of the light source is modulated by the suppression signal having the band and level to increase a threshold level at which the output light generates stimulated Brillouin scattering in the optical fiber transmission path 4 to modulate the phase or light frequency of the output light to the semiconductor laser, and the intensity modulation component of the output light generated by the modulation made by the suppression signal is thus negated by the second external modulator 8.