two input exclusive or circuits 71 and 72 the exclusive or circuits 71 and 72 produce no output and consequently the synchronization monitoring circuit 43 produces no output while the phase of the output from the oscillating circuit 29 of the pertinent triport ups 1 coincides with that of the outputs from the oscillating circuits of the other two triport ups 39 s 2 and 3 when the phase of the output from the oscillating circuit 29 of triport ups 1 deviates from that of the outputs from the oscillating circuits of the other two triport ups 39 s 2 and 3 the outputs of the pair of exclusive or circuits 71 and 72 are 34 1 39 s 34 and therefore an and circuit 73 produces 34 1 34 as an output the output 34 1 34 from the and circuit 73 as in the operation mode monitoring circuit shown in fig3 is applied to a timer circuit or delay circuit 74 and both the outputs from the and circuit 73 and the timer circuit 74 are fed to an and circuit 75 as a result the and circuit 75 produces an output when the state in which the output of the oscillating circuit 29 deviates from that of the other triport ups 39 s 2 and 3 continues beyond the prescribed duration and said output is used as a parallel release signal f for opening switch 25 generally the exclusive logical operation for the monitoring of synchronization during the parallel operation of plural triport ups 39 s can be suitably set for each in accordance with.