For a voice guidance phrase, multiple voice data items having individually different voice ranges or frequencies are previously stored in a memory. A voice mixing unit chooses to mix three voice data items among the stored voice data items and thereby produces a mixed voice data item. A voice outputting unit converts the mixed voice data item into a voice and then vocalizes a voice guidance phrase via a speaker. A voice measuring unit measures a characteristic of a frequency, a volume, or a pronunciation speed with respect to a response voice responding to the outputted voice guidance phrase. A voice mixing unit produces a mixed voice data item having a characteristic similar to the measured characteristic and outputs it.