This paper proposes one of a response production method on chatting system automatically. Our approach is applied to Japanese language. This is not necessary that it achieve a task. The responses support our conversation flow and let us produce a new topic. The system will get much information for the speaker by performing much conversation with this system. Based on the much information by a conversation with the system, the flexible reply for a speaker will come to be possible. In the present paper, we propose a response by association of the input sentence. For example, we associate "medical treatment" with "hospital". We reply then using the association word. If, like humans, a machine can reply using the association word, it will return various flexible responses.