An apparatus for transmitting an analog signal, comprising: a photocoupler configured to receive an input analog signal and transform the input analog signal into an output analog signal, which varies with the input analog signal in a manner of non-linearity; a non-linearity correcting unit configured to receive the output analog signal and correct the non-linearity to output a corrected output analog signal; characterized by an input unit to transform an input voltage signal into a current signal as the input analog signal, wherein the input unit further comprises a temperature drift compensating unit to compensate a temperature drift caused by the non-linearity correcting unit, wherein the temperature drift compensating unit comprises a compensating device, a constant current source (I S) and a compensating power amplifier (A 1) to introduce into the input voltage signal a compensating temperature drift that corresponds to the temperature drift caused by the non-linearity correcting unit, wherein the compensating device comprises at least one diode or at least one transistor, a forward input of the diode or a junction of the transistor being connected to an inverting input of the compensating power amplifier, with an inverse input of the diode or the junction of the transistor being connected to the constant current source (I S) and an analog signal source (U I), and a reference voltage (V r) being connected to a non-inverting input of the compensating power amplifier, wherein the temperature drift compensating unit further comprises a first capacitor (C 1) connected to an output of the compensating power amplifier so as to filter a DC component off the input voltage signal. a photocoupler configured to receive an input analog signal and transform the input analog signal into an output analog signal, which varies with the input analog signal in a manner of non-linearity; a non-linearity correcting unit configured to receive the output analog signal and correct the non-linearity to output a corrected output analog signal; characterized by an input unit to transform an input voltage signal into a current signal as the input analog signal, wherein the input unit further comprises a temperature drift compensating unit to compensate a temperature drift caused by the non-linearity correcting unit, wherein the temperature drift compensating unit comprises a compensating device, a constant current source (I S) and a compensating power amplifier (A 1) to introduce into the input voltage signal a compensating temperature drift that corresponds to the temperature drift caused by the non-linearity correcting unit, wherein the compensating device comprises at least one diode or at least one transistor, a forward input of the diode or a junction of the transistor being connected to an inverting input of the compensating power amplifier, with an inverse input of the diode or the junction of the transistor being connected to the constant current source (I S) and an analog signal source (U I), and a reference voltage (V r) being connected to a non-inverting input of the compensating power amplifier, wherein the temperature drift compensating unit further comprises a first capacitor (C 1) connected to an output of the compensating power amplifier so as to filter a DC component off the input voltage signal.