1. A symbol insertion apparatus for inserting a symbol in a word sequence transcribing voice information that weights symbol insertion likelihood obtained by each of a plurality of symbol insertion models for the word sequence to insert the symbol in, which are supplied for each speaking style feature according to a similarity between the speaking style feature of the word sequence and a plurality of the speaking style feature models and relevance between the symbol insertion model and the speaking style feature model, and performs symbol insertion evaluation to the word sequence.