PURPOSE: To obtain a time-division multiplex transmission controlling system which can respond quickly, by always performing one-cycle polling to measuring terminals at every appropriate cycles of polling to control monitoring terminals and storing measured data in a memory and, at the same time, immediately sending the measured data if a measurement request is made from a host computer.

CONSTITUTION: Plural terminals 3a, 3b,... and 4a, 4b,... are connected with a main control board 2 which is connected with a host computer 1, through an exclusively-used transmission line 5, and a DIP type digital switch 7 to be used for measuring the polling frequency to the measuring terminals 4a, 4b,... is installed to the main control board 2 in addition to conventional constitution. Each of the control monitoring terminals 3 is constituted by connecting a remote control relay block 18 to a general block and controls a load by using a contact output 19 in accordance with control data from the main control board 2. The terminal 3 also reads the ON/OFF state of a detector from a contact input 20 and sends the read content to the main control board 2 as monitoring data. Moreover, each of the measuring terminals 4 is constituted by connecting an AD converter to the general block and sends read measurement data to the main control board 2.