1. A symbol insertion apparatus for inserting a symbol in a word sequence transcribing voice information comprising: a symbol insertion likelihood calculation unit that obtains a symbol insertion likelihood of the word sequence for each of a plurality of symbol insertion models, the plurality of symbol insertion models being supplied for the word sequence to insert the symbol in for each speaking style feature; a speaking style feature similarity calculation unit that obtains a similarity between the speaking style feature of the word sequence and a plurality of speaking style feature models; and a symbol insertion evaluation unit, implemented by a processor, that weights the symbol insertion likelihood obtained for the word sequence for each of the plurality of symbol insertion models according to the similarly between the speaking style feature of the word sequence and the plurality of speaking style feature models and a relevance between the symbol insertion model and the speaking style feature model, and perform symbol insertion evaluation to the word sequence.