To provide a network distribution type question investigation system capable of obtaining proper answer by presenting required optional question only after an answerer answers for a basic question when the optional question is set in question document in question investigation performed on a network.

A terminal unit 10 of a person conducting investigation is provided with a conversion part 11 converting the question document 30 into distribution data 31 of special form, a terminal unit 20 of the answerer is provided with an exclusive viewer 21 reading the distribution data 31 and displaying a question sentence, the conversion part 11 records the information related to independence relation among questions and presentation conditions of the optional question in the distribution data 31 when the optional question is set in the question document 30 to be converted into the distribution data 31, and the viewer 21 displays the basic question only initially in accordance with the information related to the dependence relation among questions recorded in the distribution data 31 and the presentation condition of the questions and displays the optional question in accordance with the contents of the answers for the questions.