The present invention is intended to achieve a transconductance amplifier and a voltage/current converting method which can provide a sufficient amplitude and a high degree of design freedom. The method comprises the steps of converting a first voltage signal to a first current signal; converting a second voltage signal to a second current signal; obtaining the common-mode components of the first and second current signals; and subtracting the common-mode components from the first and second current signals to obtain third and fourth signals, and further, subtracting the fourth current signal from the third current signal to generate a first output, while subtracting the third current signal from the fourth current signal to generate a second output.