PURPOSE: To control the connecting/disconnecting state of a terminating resistor at a slave station from a master station.

CONSTITUTION: When a master station 100 in a monitor room A is moved to the vicinity of a terminal equipment 501, a terminating resistor ON instruction is sent from the master station 100 to a terminal equipment 500. When this instruction is received, a coil 112 is excited through a terminating resistor control part 11, a contact 113 is turned on, and a terminating resistor 43 is turned to the connecting state. A switch 44 of a converter 200 at the master station is manually turned off, and the terminating resistor is turned to the disconnecting state. The master station is connected adjacently to the terminal equipment 501. When the master station connected adjacently is returned to the terminal equipment 501 to the monitor room, a terminating resistor OFF instruction is sent from the master station to the terminal equipment 500. The terminal equipment 500 receives this instruction, the coil 112 is demagnetized through the terminating resistor control part 111, the contact 113 is turned off, and the terminating resistor is turned to the disconnecting state. The switch of the converter at the master station is manually turned on, and the terminating resistor is turned to the connecting state. The master station is installed at the monitor room.