1. A pattern-detection apparatus that detects a specific pattern contained in an image, said pattern-detection apparatus comprising: a binarizing unit that binarizes an input image to obtain binary image data, a partial-image recognition unit that recognizes a partial image that is contained in said binary image data, and that is part of said specific pattern and has an empty inside, and a specific pattern determination unit that determines the said specific pattern contained in said image, based on the recognition results obtained by said partial-image recognition unit, wherein said partial-image recognition unit successively scans, for said binary image data, a pixel-block area of predetermined size containing an target pixel, and said partial-image recognition unit recognizing a partial image contained in said binary image data, on the condition that at least one OFF-pixel exists within a reference block consisting of said target pixel and predetermined pixels in its neighborhood within said pixel-block area.