PURPOSE: To easily cope with the color change of a measurement subject by converting the signal obtained from the synchronous detection into a digital signal, applying this digital signal to a memory as an address signal, and extracting a specific color based on the memory contents for recognition of a shape.

CONSTITUTION: A chrominance signal separator 3 separates an input signal CS and outputs a chrominance signal S1 and a luminance signal S2 to a synchro nous detection circuit 4 and an A/D converter 5 respectively. The circuit 4 separates the signal S1 into a signal (R-Y) and a signal (B-Y) with execution of the detection and outputs these separated signals to the A/D converters 6 and 7 respectively. Then a memory 10 works with the digitized signals (R-Y) and (B-Y) used as the address inputs and stores the data on the color of an extraction subject. A digitized luminance signal is selected in response to the output of the memory 10 for recognition of a shape. Thus various colors are extracted out of the subject according to the width and the conditions of an optional color for decision of a shape.