A contiguous word recognizing unit recognizes speech as a morpheme string, based on an acoustic model and a language model. A sentence obtaining unit obtains an exemplary sentence related to the speech out of a correct sentence storage unit. Based on the degree of matching, a sentence correspondence bringing unit brings first morphemes contained in the recognized morpheme string into correspondence with second morphemes contained in the obtained exemplary sentence. A disparity detecting unit detects one or more of the first morphemes each of which does not match the corresponding one of the second morphemes as disparity portions. A cause information obtaining unit obtains output information that corresponds to a condition satisfied by each of the disparity portions out of a cause information storage unit. An output unit outputs the obtained output information.