An error detecting device of a dual controller system is provided. The first controller receives a sensing data from a sensor to calculate and generate a first data and outputs a final data if an error is not detected by comparing the first data with a second data transmitted from a second controller. The CAN transceiver receives the final data from the first controller and transmits the final data through a CAN bus. The second controller receives the sensing data from the sensor to calculate and generate a second data and transmits to the first controller an interrupt signal which prevents an output of the final data if an error is detected by comparing the second data with the final data fed back from the CAN transceiver. Accordingly, output transmission to the vehicle is controlled and the stability and reliability of the output data is increased.