An apparatus, comprising: a control unit; a relay unit comprising a first switch configured to set the relay unit into open or closed state by control of the control unit, the relay unit through which the current of the battery flows in closed state to supply the power; the apparatus is characterised by: a parallel unit connected to an input terminal and an output terminal of the relay unit as a parallel circuit, comprising a second switch configured to set the parallel unit into open or closed state by control of the control unit, and applies the current of the battery in closed state instead of the relay unit in open state in which the power supply is stopped; a parallel unit voltage sensing unit which senses the voltage of the parallel unit and outputs the same to the control unit; and a parallel unit current sensing unit which senses the current of the parallel unit and outputs the same to the control unit, wherein the control unit is configured to control into first state in which the relay unit is in closed state and the parallel unit is in open state, and when voltage and current of the parallel unit is 0 in the first state, control into second state in which the relay unit is in closed state and the parallel unit is in closed state, and when the voltage of the parallel unit is equal to voltage of the battery and the current of the parallel unit is 0 in the second state, control into third state in which the relay unit is in open state and the parallel unit is in closed state, and when the current of the parallel unit is equal to current of the relay unit in the third state, the control unit determines the first switch to be normal, and when the current of the parallel unit is 0, the control unit determines the first switch to be faulty. a control unit; a relay unit comprising a first switch configured to set the relay unit into open or closed state by control of the control unit, the relay unit through which the current of the battery flows in closed state to supply the power; the apparatus is characterised by: a parallel unit connected to an input terminal and an output terminal of the relay unit as a parallel circuit, comprising a second switch configured to set the parallel unit into open or closed state by control of the control unit, and applies the current of the battery in closed state instead of the relay unit in open state in which the power supply is stopped; a parallel unit voltage sensing unit which senses the voltage of the parallel unit and outputs the same to the control unit; and a parallel unit current sensing unit which senses the current of the parallel unit and outputs the same to the control unit, wherein the control unit is configured to control into first state in which the relay unit is in closed state and the parallel unit is in open state, and when voltage and current of the parallel unit is 0 in the first state, control into second state in which the relay unit is in closed state and the parallel unit is in closed state, and when the voltage of the parallel unit is equal to voltage of the battery and the current of the parallel unit is 0 in the second state, control into third state in which the relay unit is in open state and the parallel unit is in closed state, and when the current of the parallel unit is equal to current of the relay unit in the third state, the control unit determines the first switch to be normal, and when the current of the parallel unit is 0, the control unit determines the first switch to be faulty. a parallel unit connected to an input terminal and an output terminal of the relay unit as a parallel circuit, comprising a second switch configured to set the parallel unit into open or closed state by control of the control unit, and applies the current of the battery in closed state instead of the relay unit in open state in which the power supply is stopped; a parallel unit voltage sensing unit which senses the voltage of the parallel unit and outputs the same to the control unit; and a parallel unit current sensing unit which senses the current of the parallel unit and outputs the same to the control unit, wherein the control unit is configured to control into first state in which the relay unit is in closed state and the parallel unit is in open state, and when voltage and current of the parallel unit is 0 in the first state, control into second state in which the relay unit is in closed state and the parallel unit is in closed state, and when the voltage of the parallel unit is equal to voltage of the battery and the current of the parallel unit is 0 in the second state, control into third state in which the relay unit is in open state and the parallel unit is in closed state, and when the current of the parallel unit is equal to current of the relay unit in the third state, the control unit determines the first switch to be normal, and when the current of the parallel unit is 0, the control unit determines the first switch to be faulty.