A signal control apparatus comprises: a first delay unit that receives a modulated signal corresponding to a positive input signal component; a second delay unit that receives a modulated signal corresponding to a negative input signal component; transducers that receive signals from the delay units and that output, as ultrasonic waves, the received signals; a microphone that detects the ultrasonic waves outputted from the transducers; a waveform characteristic detection unit that integrates the detected ultrasonic waves, thereby detecting the waveform characteristics of the positive sonic wave and of the negative sonic wave; and a delay adjustment unit that inputs, based on the detected waveform characteristics, to the first delay unit or second delay unit, the information of a delay amount being in accordance with a phase difference between the signal outputted from the first delay unit and the signal outputted from the second delay unit to reduce the phase difference.