Each of a plurality of redundantly formed semiconductor circuits integrally has a monitor transistor and is energized by being supplied with an enable signal. A monitor circuit associated with each semiconductor circuit detects a collector current of the monitor transistor and, when the collector current is less than a predetermined threshold value, outputs an alarm signal. A variation predicting circuit calculates the rate of change per unit time with respect to the collector current. An order determining circuit stores the identification numbers of the semiconductor circuits into an order determination register in descending order of the rate of change. The order determination register initially outputs the front identification number, and thereafter outputs the respective following identification number each time a respective one of the monitor circuits outputs an alarm signal. A semiconductor circuit selection decoder supplies an enable signal to the semiconductor circuit indicated by an identification number.