To make it possible to hold a value which has been output by an equipment just by removing the equipment by monitoring a power supply of the equipment at all times by means of an inverter and outputting an analog value to correspond to a supply voltage on a control output signal from a counter.

Counters 4A, 4B, being connected to an inverter 1 and a clock 3, start operation on a signal from the inverter 1 and holds a counter value to correspond to the discharging voltage of a capacitor 2 and a clock frequency from the clock 3. To be more specific, the inverter 1 monitors a power supply of an equipment at all times and when the power supply is out off due to the removal, etc., of the equipment, a capacitor 2 which has been charged with an output value of the equipment starts discharging and the discharging amount is held by the counters 4A, 4B by the clock 3 from an oscillating circuit. Then, analog switches 5A, 5B to correspond with the held value are turned on and thereby the same value as has been output from a system power circuit 6 is output and that value can be held.