A terminal box is provided to connect an error meter to a terminal of a phase voltage display unit without removing a sealing structure of a terminal box cover in order to measure an error meter. A current detector(110) detects a current of each phase through a CT(Current Transformer). A voltage detector(120) detects a voltage of each phase through resistance. An MOF(Metering Output Fit) protecting unit(130) detects an MOF output voltage or current to determine and protect an erroneous line. An erroneous line display unit(160) displays an erroneous line state. A reverse phase display unit(170) displays an reverse phase. A voltage current display device(180) per a phase displays a voltage and a current per a phase. A controller(150) controls each unit.
