PURPOSE: To improve both the accuracy and the linearity, by modulating an input current from a light emitting element in an analog optical transmission converter of direct intensity modulation system with a triangular wave having a frequency higher than the frequency of the signal to be transmitted.

CONSTITUTION: The signal to be transmitted is fed to an input terminal 1 and then amplified 2 to be applied to a modulator 11. A triangular wave generator 10 feeds a triangular wave having a frequency higher than the upper limit of the frequency of the signal to be transmitted to the modulator 11 as a modulated signal. The modulator 11 adds the signal to be transmitted and the product of the triangular wave and feeds them to the signal to be transmitted. With such modulation applied to the signal to be transmitted, the distribution of the voltage-reside time factor of the modulated output signal is made uniform within a modulated amplitude section since the modulated signal has a triangular waveform. As a result, the scattering effect is increased for the nonlinearity of a light emitting element. This facilitates greatly the signal correction with use of a negative feedback loop. Thus a highly accurate electric-optical signal conversion is possible.