A client computer installs a plurality of functions in advance, and the client computer accesses a server computer to inform a function desired to be used to the server computer. The server computer charges the price of the informed function to a user, and transmits the fact to the client computer. By removing the function limitation of the charged function, the client computer becomes possible to use the function. Consequently, because the user can use a necessary function by paying only the price of the function, the user can save the costs of the use. Moreover, because the user is not required to download a new function, the user can save time.