Disclosed is a signal output circuit. According to the signal output circuit, an input buffer receives a single phase changing-over command signal from external, converts the single phase changing-over command signal to a difference changing-over command signal which is formed by two signals mutually opposite in phases, and outputs the difference changing-over command signal. The single phase changing-over command signal is used for commanding that a status of the output circuit is changed to one of a forbidden turn-off status and a start turn-off status. Based on the difference changing-over command signal, a generated control circuit outputs a generated control signal which is used for controlling of generation of a control voltage in a control voltage generating circuit. Based on the generated control signal, the control voltage generating circuit outputs the control voltage, and changes value of the control voltage according to logic of the single phase changing-over command signal. The output circuit receives the difference changing-over command signal from the external, conducts impedance conversion to the difference changing-over command signal, outputs a difference output signal, and based on the control voltage, switch between the forbidden turn-off status and the start turn-off status of the difference output signal.