A signal drive apparatus includes a first buffer circuit where a signal converted into an electric signal from a first light signal is amplified; a second buffer circuit where a signal converted into an electric signal from a second light signal is amplified; a control circuit causing one of the first and second buffer circuits to be in an operating state and causing an output stage of the other buffer circuit to be in an idle state of a high impedance, so as to output a changeover control signal which picks up either the first or the second light signal; and a voltage changeover circuit causing any one of the output stages of the first and the second buffer circuits to be in the idle state and supplying a transistor constituting the output stage with a bias voltage equal to or less than a withstand voltage of the transistor.