A retrieval system enables high-speed and high-precision pattern retrieval. A retrieval dictionary generation unit classifies learned patterns into plural clusters, and generates a retrieval dictionary using the clusters. A nearest cluster detector detects, a cluster nearest to an input retrieval patter from among clusters in a multidimensional space. The specific space is generated between a couple of spheres having radiuses smaller and larger, respectively, than a distance from a central cluster that locates near the center of the multidimensional space to the retrieval pattern. A learned pattern detector compares all learned patterns that belong to the nearest cluster with the retrieval pattern and detects a learned pattern at predetermined distance from the retrieval pattern. A retrieval range decision unit decides a retrieval range using the learned pattern detected by the learned pattern detector and retrieval pattern.