PURPOSE: To secure the continuity of control by eliminating the switching of controller at the time of the failure of a data transmitting equipment.

CONSTITUTION: This data transmitting equipment is provided with active system and stand-by system data transmission processing means 18A-B, 19A-B, 20A-B, 21A-B, 22A-B and 23A, 23B for executing the transmission processing of data received from a control device 15a or transmission lines 13a, 13b, transmission abnormality detecting means 19A, 24A for detecting the existence of transmission processing abnormality in the active system data transmission processing means based upon programs and data in the active system data transmission processing means and a transmission system switching means 17, 26 for connecting only the active system data transmission processing means to the controller 15a and the transmission lines 13a, 13b, and abnormality in transmission processing is detected by the abnormality detecting means, disconnecting the active system data transmission processing means from the control device 15a and the transmission lines 13a, 13b and connecting stand-by system data transmission processing means to the controller and the transmission lines.