A reflection optical modulator including a bidirectional optical amplifier, or a multi-wavelength simultaneous optical modulating device composed by combining reflection optical modulators. BY numerically limiting the relation between the gain of the bidirectional optical amplifier and the loss of the optical modulators or by inserting polarization rotating means, the influence of the light reflected at the ends of the bidirectional optical amplifier is lessened, and a stable amplifying function is realized. A transmission optical modulator including semiconductor optical amplifiers (SOAs) connected in multiple stages is also disclosed. Optical isolators are inserted every other SOAs. Thus, the influence of the reflected light is lessened, and a stable amplifying function and reduction of the cost are both realized.