PURPOSE: To perform the conversion and the decision of the Japanese word character strings in accordance with the treatment relation by inputting the treatment relations of seniors and juniors to be meant by the Japanese word character strings.

CONSTITUTION: A Japanese word input part 1 inputs the Japanese word character strings, and a Japanese word storage part 2 stores temporarily the Japanese word character strings inputted via the part 1. A treatment relation analyzing part 8 reads the Japanese word character strings out of the part 2 and outputs the information on the treatment relation shown by the Japanese word character strings. A 1st treatment relation temporary storage part 9 stores temporarily the information on the treatment relation outputted from the part 8. A treatment relation input part 10 inputs the information on the treatment relation. A 2nd treatment relation temporary storage part 11 stores temporarily the information on the treatment relation inputted by the part 10. Then a treatment relation comparing part 13 compares the treatment relations temporarily stored in both parts 9 and 11 with each other and outputs the result of comparison. In such a constitution, the honorific expressions of sentences consisting of Japanese word character strings can be converted into the expressions subject to the treatment relation to be shown in the honorific expressions.