An information sharing system includes a computer network formed of terminals and a server and allows information about a posted message to be shared among users. The system or a terminal acquires a question message input via the terminal together with positional information associated with the question message and causes the acquired question message to be accessible to the users. The system or terminal acquires an answer message input by a respondent via the terminal as an answer to the question message and causes the acquired answer message to be accessible to the users. The system or terminal acquires positional information of the respondent and restricts the respondent accessing the question message on the basis of question positional information that is the positional information associated with the question message and respondent positional information that is the acquired positional information of the respondent.