To extract data efficiently from plural terminals at a remote place.

Each terminal C1 having data to be extracted starts a local reply function 15a, which generates, e.g. a random number. A central controller 1 transmits information to designate a numerical range to each terminal C1. Each terminal C1 discriminates whether or not a random number being an output of its own local reply function 15a is within the numerical range received from the central controller 1. If the random number is set within the designated numeral range, the terminal C1 sends data stored in its own device to the central controller 1. Then the central controller 1 analyzes the received data, transmits a decided threshold to all the terminals and only the terminal having data in excess of the threshold replies it and sends the data.