PURPOSE: To suppress a transmission error owing to the collision of data on a transmission line even if plural telemeter slave stations are simultaneously called by shifting telemeter slave station start time by micro timing through the use of random numbers.

CONSTITUTION: A data call part 1 requests the call of the telemeter slave station for collecting data from the plural telemeter stations 3. A line control part 2 receiving the call request of the telemeter slave station controls a random delay function part 6. It generates telemeter salve station call start timing which is shifted by micro timing by using the random numbers, and transmits it to the line control part 2. It calls the plural telemeter salve stations 3 in accordance with the received telemeter slave station call start time which is shifted by micro timing.