Abstract: A network data distribution system which is operated, under circumstances affected by external or internal factors, without discontinuing a data distribution service while being adapted to the present situation is provided. In the server side of the system, data requested from a client are divided into packets, and packet data is formed by adding a time index, and in the client side, an amount of transmission or processing delay is calculated based on the time index included in the received packet data, and delay time information based on the calculated result is communicated. The server side selects the packet data to be next transmitted based on the communicated delay time information, and sends the selected packet data.