Converting circuits convert the values of multiple items of SD pixel data (pixel value) as class tap data to luminance values. The converting circuits convert pixel values to luminance values based on a correspondence relation between a value of pixel data in an image display device and a luminance value. Class-detecting circuits detect a space class and a motion class based on plural luminance values. Class-synthesizing circuit acquires a class code indicating the class to which the pixel data of a target position in an HD signal belongs. Estimation/prediction-operating circuit obtains items of pixel data of the target position in the HD signal based on an estimation equation using data of an prediction tap and coefficient data of the class indicated by the class code. Consequently, appropriate classification of class to the luminance characteristic of a display device is performed.