To promote fixing of a past questioner's knowledge while preventing concentration of questions to a specific user by setting the past questioner as a responder in an information processing system for managing exchange of questions and answers between users.

A theme knowledge retrieval part 113 retrieves a user DB 121 in response to a theme intellectual person retrieval request from a user terminal 205, and retrieves a user A having knowledge for a designated theme. A question part 114 receives a question sentence to the user A retrieved by the retrieval part 113 from the user terminal 205, examines whether the user A has answered the same question sentence in the past or not in reference to a question-answer DB 122, determines a responder D from the past questioners thereto when the user A has answered the same question sentence, and outputs the question sentence to a user terminal 204 of the determined responder D.