The activity information accounting system stores an account title table corresponding to activity information, and performs accounting procedures on the basis of an input activity information and an account title corresponding to the input activity information. The accounting system displays activity types including purchase and acquisition activity, sales and revenue activity, expenditure activity, investment and finance activity, and production activity. If user selects one of the displayed activity types, the accounting system displays a screen for the user to input activity information for the selected activity type. The accounting system determines if the input activity information is internal activity or external activity, performs accounting procedures on the basis of determined result and the account title table.