The invention relates to fault detection device in power industry, in particular to a fault detection device operating a low-voltage current transformer. The fault detection device comprises two insulation operating rods, wherein the bottom end of each insulation operating rod is provided with a handle, each top end is provided with a connecting piece, each connecting piece is provided with a conductive clamp, a threaded hole is formed in each connecting piece, a screw rod is matched in each threaded hole, a sleeve pipe is arranged in each insulation operating rod, two ends of each sleeve pipe are respectively connected with the corresponding screw rod and the corresponding handle, a guide rail is arranged between the insulation operating rods, each insulation operating rod is provided with a guide rail connector, the guide rail connectors are arranged on the rail of the guide rail in a matched manner, a current indicator is fixed on the guide rail, and the current indicator is connected with the connecting pieces through lead wires. The fault detection device can short-circuit a secondary side of the current transformer in an electrified condition safely and conveniently, monitors changes of current of the secondary side through the current indicators, and judges whether the current transformer operates normally or not.