To perform proper maintenance of an internal combustion engine on the basis of cumulative number of revolution of the engine and to more exactly obtain operational status of the internal combustion engine or an electric motor since deterioration in the engine, various belts and oils is considered to be proportional to the actual driving hours of the engine, however a tachometer mounted for the internal combustion engine or a rotational speed meter mounted for the electric motor in most automobiles is a meter showing the number of revolution in a unit time, and hence a user can not confirm the integrated value of the number of revolution.

The number of revolution of the internal combustion engine or the electric motor detected by a number of revolution detection part A1 is accumulated by a cumulative calculation part A2 to enable the user to easily recognize the integrated number of revolution through an integrated value display part A3. Thus, it is possible to properly perform various maintenance.