PURPOSE: To prevent an erroneous display, by providing a discriminating circuit to detect the correct working of each element of a display device based on the signal given from a display meter driving circuit.

CONSTITUTION: When the lubrication is desired for example, a nozzle valve 15 is detached from a nozzle hook 42 to start the lubrication. The lubrication is measured by a flowmeter 12, and the pulse signal is supplied to a 0.1l counter circuit 20. The circuit 20 starts the binary counting with supply of the pulse signal, and the driving signal displaying the figure is produced at seven circuits. This driving signal current flows to either one of the coils 2 and 3 of the seven elements 7 at a 0.1l digit display part 21. Thus a figure corresponding to the signal is displayed. Then the signals supplied from a display meter driving circuit 29 and a temporary storing circuit 22 are fed into exclusive OR circuits 42W48. The OR circuits corresponding to the display elements produce the signals. Then the correct driving is discriminated by the OR circuit 41 via the OR circuits 34W40. In such way, an erroneous display is prevented.