PURPOSE: To make a branching circuit economical by providing a detection circuit giving a part of an input signal to one differential input, collecting part of output signals of an output circuit, giving the result to the other differential input and outputting an alarm signal at the time of detecting the abnormality of a signal.

CONSTITUTION: A branch output circuit 1 branching an input signal into a prescribed number for the output, output circuits 21∼2n outputting each branch signal of the circuit 1 and the detection circuit 5 giving part of the input signal to one differential input an collecting the parts of the output signals of the output circuits 21∼2n, giving the result to the other differential input and raising an alarm in detecting the signal fault, are provided. An adder circuit 4 adds a part of outputs (branch signals) OUT1∼OUTn of the output circuits 21∼2n. The branch signals OUT1∼OUTn are subjected to weighting to recognize which branch signal has the abnormality. The abnormality detection circuit 5 is used in common to attain the economical branch circuit.