PURPOSE: To input a speed stage into a data recorder correctly by providing a voltage generator for outputting a voltage corresponding to the segment signal of a shift indicator controller, and detecting the speed stage based on the output voltage.

CONSTITUTION: A speed stage signal is inputted by a shift lever 1 into a transmission controller 2. The speed of the transmission 3 is changed into the corresponding speed stage based on the signal. The signal is inputted into a shift indicator controller 4, and the speed stage is displayed on a monitor 5. For example, oil pressure is supplied to a clutch and the speed is changed with the transmission 3. The speed stage signal is inputted into the controller 4 through a pressure switch which is turned ON with the oil pressure. The controller 4 sequentially inputs the segment signal corresponding to the input speed- stage signal into an isolator 6, a selector 7, a voltage selector 8 and a voltage generator 9. The voltage corresponding to the speed stage is outputted through an addition amplifier 10. The speed stage is detected based on the output voltage.