An overflow suppression technique that is effective for avoiding degradation in image quality is provided. A fundamental waveform and detail is extracted out of an input RGB signal. A suppression gain generation unit 614 generates a suppression gain from the extracted fundamental waveform. Multipliers 612a and 612b multiply the detail and the fundamental waveform by the generated suppression gain, respectively. Then, an adder 626 combines them together for a mixed output. Alternatively, equalization processing is performed as follows. A low frequency component fundamental waveform is obtained as a result of the passing of an input RGB signal through a low pass filter 622. A suppression gain is generated from the low frequency component fundamental waveform. Then, the input itself is multiplied by the suppression gain to obtain an output.