A multimedia information system comprises first and second communication terminal apparatuses for exchanging information data using a common first communication protocol or first and second communication protocols which are different from each other, a first communication network for transmitting information data in accordance with a third communication protocol different from the first and second communication protocols, and first and second communication interface apparatuses for respectively connecting the first and second communication terminal apparatuses to the first communication network, the first communication interface apparatus comprises first conversion means for converting information data in accordance with the first and third communication protocols between the first communication terminal apparatus and the first communication network, and the second communication interface apparatus comprises second conversion means for converting information data in accordance with the second and third communication protocols between the second communication terminal apparatus and the first communication network.