A data transmission device (1) includes a controller (2), a reception section (5), a transmission section (6), and an MPU (3). The reception section (5) receives an electric signal sent from a preceding device, and outputs its data to the controller (2). The transmission section (6) converts a result of a process by the controller (2) into an electric signal and transmits it to a successive device. The MPU (3) controls operation of the controller (2), the reception section (5), and the transmission section (6) in accordance with the operation mode of the device. The reception section (5) detects cessation of the electric signal sent from the preceding device and, in response to the detection, stops operating. In response to the detection, the transmission section (6) stops operating and stops sending the electric signal to the successive device.