1. A template matching method of detecting the position of an image region similar to a template image region from on a reference image, comprising: calculating the similarity of the image region to the template image region at rough position intervals; estimating the similarity at a position, where the similarity is not calculated, making use of the directional gradients of similarity obtained independently in a plurality of directions from the calculated values of similarity; and determining the position having a small calculated or estimated value of the similarity as the position of the similar image region.