A specific color detection circuit shows an RGB input pixel and an RGB color signal to be detected in a three-dimensional coordinate, calculates a first distance from an origin to a foot of a perpendicular drawn from the coordinate of the RGB input pixel to a straight line connecting the origin and the coordinate of the RGB color signal or a coordinate with the same RGB ratio as the signal and a second distance from the coordinate of the input pixel to the foot, and detects a hue of a signal of the input pixel. The circuit generates a detection region in a color-difference direction according to the first distance and the hue, calculates a third distance based on the first distance for the detection region and judges the input pixel as being in a predetermined color detection region when the third distance is longer than the second distance.