A plurality of reference words based on a second distance index that allows coding of a first distance index are registered in an associative memory core in advance. In a first pipeline stage, a retrieved word having a predetermined number of bits is extracted from input data in a predetermined clock cycle, and the retrieved word is coded with the second distance index and output to the core. In a second pipeline stage, the core searches for a reference word inhabiting the largest similarity with respect to the retrieved word (winner) obtained in the previous clock cycle. In a third pipeline stage, the core output result in the previous clock cycle is analyzed, one winner is determined on the basis of a specific priority, and an address indicating the location of the winner and the distance between the input data and the winner are coded and output.