PURPOSE: To prevent the defective work without feeding back an abnormal load voltage value by intermitting the output of an electric power for working at the time of occurring the abnormality in the load voltage value caused by the abnormal connection of a load voltage detecting line and outputting the electric power to an abnormal connection display circuit too thereby displaying the accurrence of abnormal connection in the load voltage detecting line.

CONSTITUTION: In a detecting line defect discrimination circuit AN, a comparing signal Cm and an output command signal Na are subjected to logical operation and the abnormal connection in the loaded voltage detecting line 5 is discriminated to output a detecting line defect discrimination signal An. In a discrimination holding circuit HD, the detecting line defect discrimination signal An is inputted and held to output a discrimination holding signal Hd. In the abnormal connection display circuit DS, the discrimination holding signal Hd is inputted to display the abnormal connection. In an electric source output discrimination circuit NA, an output command input signal In from an output command signal input terminal IN and the discrimination holding signal Hd are inputted to discriminate whether the operation is normal or abnormal. At the time of the normal operation, the output command signal Na is outputted and at the time of the abnormal operation, the output command signal Na is intermitted.