PURPOSE: To detect the recognition parameter with higher accuracy than the resolution of an input image at the time of generalized Hough transform.

CONSTITUTION: With respect to a gradation image, a distance (rj) of a feature point and a reference point and an azimuth j are stored in an address position of a reference table and from the gradation value data (rj) and the j value of each picture element (x, y) of the gradation image, signals (x), (y) of an address generator 2, a signal θ of an angle generator 10, and a signal (s) of a size fluctuation correction rate generator 11, the address transform of x+ s×rjocos(θ+j) and y+s×rjsin(θ+j) is executed by an address transform part 5. A reciprocal ratio of a distance between a candidate point (xG', yG', θs) and the corresponding point of an adjacent address is accumulated in an adjacent address position on a parameter accumulation memory 8 by an accumulation arithmetic part 7, a temporary maximum point being above a prescribed threshold is determined from accumulated data, the accumulated data of an adjacent address in the periphery of the maximum point is inputted, an interpolating operation is executed and a position of the maximum point is determined by a parameter determining part 12.