A speech recognition apparatus that requires a reduced amount of computation for likelihood calculation is provided. A language lookahead score for a node of interest is generated based on the language scores for each recognition word shared by the node of interest. To this is added the node's acoustic score, which is calculated based on the likelihood of the connected hypotheses expressed by a path from the root node to the parent node of the node of interest. From this added result, the language lookahead score resulting when the parent node is the node of interest is deleted, and the language lookahead score is updated by adding the language lookahead score of the node of interest. The updating of the language lookahead score is terminated at a specific position in the tree structure.