PURPOSE: To enable to make the capacity of a backup capacitor small by decreasing the output current of a meter driving circuit by a signal from a zero resetting circuit at the time of an electric power source off.

CONSTITUTION: The output of a circuit 1 that converts an input frequency to DC signal voltage is connected to the input of the meter driving circuit 2 and a meter 3 is connected to the output. A backup capacitor 5 of which another end is grounded and the cathode of a diode 6 are connected to the power source terminals of the circuit 2 and zero resetting circuit 4, and the anode side is connected to the power source 8 together with the power source terminal of the circuit 1 and the input terminal of the circuit 4, and the zero resetting signal output terminal of the circuit 4 is connected to the zero resetting input terminal of the circuit 2. When the power source is cut off by a switch 7, the circuit 4 detects the abrupt attenuation of voltage of the input terminal and decreases the current consumption of circuits 2, 4 in the period in which the output levels of the circuit 2 are made small. Thus, the capacity of the capacitor 5 can be made small.