To provide a transformer for measurement which can ensure superior reliability and avoid the need for using double detectors and transformers to realize a low cost.

An operating circuit 5 is connected to transformers 4a, 4b, 4c and 4d. The operating circuit 5 is arranged to input secondary output Ou, Ov, Ow and Oz from the transformers 4a, 4b, 4c and 4d and to output secondary outputs to an external control/protection device or the like. when a detector 2a or transformer 4a for a U phase becomes faulty, the operating circuit 5 is designed so as to output a value obtained by subtracting the sum of the secondary output Ov for a V phase and the secondary output Ow for a W phase from a zero-phase output Oz, that is, Oz-(Ov+Ow), as a secondary output for the U phase.