PURPOSE: To improve the picture detection processing speed by incentively obtaining a correlation value on all positions near the maximum correlation value of the correlation value at random positions.

CONSTITUTION: A calculation part 12 uses the 1st function and obtains the correlation value on the picture element part of the part of color arrangement of checkered pattern. The correlation value in all picture element part in the constant range near the picture element part obtaining the maximum correlation value from among the correlation values is obtained by means of the 2nd function. The position detection corresponding to the picture element part obtaining the maximum correlation value from among the correlation values obtained by the function is performed. In short, the correlation value at the position alternately placed for the picture data to be tested is obtained by the specification of an address specification part 11 based on the normalizing calculation. The position in which the maximum correlation value is calculated is obtained from the calculation result. Then, the correlation value of each position expanded by, for example, 2×2 range in all directions from the obtained position is taken by the normalizing correlation calculation. The position in which the maximum correlation value calculated is taken as the detection position in the calculation result.