Abstract: An improvement in protecting information transmitted via a network from illegal copying is disclosed. While data input from an information provider via a network is stored in a storage device, an ID inherent in an information terminal unit stored in a ROM, the time information which is output from a real-time clock counter, an ID of the owner of an ID card read by a card reader are multiplex-recorded as identification information on the input data. Identification information is also multiplex-recorded on the data read from the storage device and to be output through the output terminal.