To provide a malfunction detection system for a current transformer for a measuring instrument, which detects the malfunctions of the current transformer for a measuring instrument to immediately take countermeasures for prevention of serious accidents in an electric power system.

A partial discharge detector 1 and a voltage sensor 7 are each connected to a monitor 3 which is further connected to a transmission device 4 through a communication line. The transmission device 4, a user terminal 5 and a maker terminal 6 are connected through a network. The partial discharge detector 1 is a device for measuring discharge noise and vibration which are generated with the occurrences of partial discharge in the externally mounted current transformer 2. The voltage sensor 7 is for measuring voltage across a reactance element 9 which is connected to the voltage detecting terminal 8 of an oil-filled current transformer 10.