A signal processing apparatus comprises: an audio signal detection circuit which detects a specific audio signal from a broadcasting program including an image signal and an audio signal; a control unit which controls an image processing processor, wherein the audio signal detection circuit generates a control signal for controlling the control unit when the audio signal detection circuit detects the specific audio signal, and the control unit controls the image processing processor according to the control signal so as to display a specific image and/or text by synthesizing the specific image and/or text corresponding to the specific audio signal and an image of the broadcasting program displayed according to the image signal.