A fault detection device includes an interface electrically connected to an electrical instrument to transfer commercial power to the electrical instrument, transmit a command for driving one of a plurality of loads included in the electrical instrument to the electrical instrument, and detect current flowing in one of the plurality of loads of the electrical instrument; and a terminal configured to receive a current signal corresponding to the current flowing in one of the plurality of loads from the interface, determine whether the one load has a fault on the basis of the received current signal and display whether the load has a fault. A faulty load is determined by detecting current of only a load suspected to have a fault when a fault is generated in the electrical instrument so as to improve fault detection accuracy.