Provides a one-terminal effector having an input terminal and an output terminal structured as one terminal by providing a circuit that makes input and output of the effector common. The one-terminal effector can avoid complex cable wiring, and can prevent degradation of sound quality. The one-terminal effector includes one input/output terminal, and an effector circuit that executes a predetermined processing on an analog audio signal that is input from the input/output terminal, and outputs the processed analog audio signal from the input/output terminal. The one-terminal effector further includes an input/output signal conversion circuit that converts the input signal and the output signal into mutually different signal forms of voltage signals or current signals.