A switch diagnosing apparatus, which diagnoses a charging switch and a discharging switch provided on a charging and discharging path of a cell assembly and connected in series with each other, the charging switch and the discharging switch being field effect transistors, FET, each connected in parallel with a parasitic diode and wherein the parasitic diodes of the charging and discharging switches are coupled anti-serially to each other, the apparatus comprising: a voltage measuring unit configured to measure both-end voltages of the charging switch and the discharging switch, respectively; a current measuring unit configured to measure a current flowing through the charging and discharging path; a processor configured to selectively control the charging switch and the discharging switch to be opened or closed, receive a measured voltage value from the voltage measuring unit, receive a measured current value from the current measuring unit, and diagnose a state of at least one of the charging switch and the discharging switch as at least one of a normal state, an open stuck state, a closed stuck state and a drift state based on at least one of the measured voltage value and the measured current value, wherein the drift state is a state where a turn-on state resistance of the switch is changed; and a diagnosis power unit having one end electrically connected to the charging and discharging path to supply a diagnosis power to at least one of the charging switch and the discharging switch; characterized in that the processor is configured to: calculate a normal state both-end voltage difference of the charging switch and a normal state both-end voltage difference of the discharging switch based on current information of the diagnosis power output by the diagnosis power unit and previously stored turn-on state resistance of each of the charging switch and the discharging switch, diagnose whether the state of the charging switch is the open stuck state based on the comparison result of the both-end voltage difference of the charging switch and the calculated normal state both-end voltage difference of the charging switch, and diagnose whether the state of the discharging switch is the open stuck state based on the comparison result of the both-end voltage difference of the discharging switch and the calculated normal state both-end voltage difference of the discharging switch. a voltage measuring unit configured to measure both-end voltages of the charging switch and the discharging switch, respectively; a current measuring unit configured to measure a current flowing through the charging and discharging path; a processor configured to selectively control the charging switch and the discharging switch to be opened or closed, receive a measured voltage value from the voltage measuring unit, receive a measured current value from the current measuring unit, and diagnose a state of at least one of the charging switch and the discharging switch as at least one of a normal state, an open stuck state, a closed stuck state and a drift state based on at least one of the measured voltage value and the measured current value, wherein the drift state is a state where a turn-on state resistance of the switch is changed; and a diagnosis power unit having one end electrically connected to the charging and discharging path to supply a diagnosis power to at least one of the charging switch and the discharging switch; characterized in that the processor is configured to: calculate a normal state both-end voltage difference of the charging switch and a normal state both-end voltage difference of the discharging switch based on current information of the diagnosis power output by the diagnosis power unit and previously stored turn-on state resistance of each of the charging switch and the discharging switch, diagnose whether the state of the charging switch is the open stuck state based on the comparison result of the both-end voltage difference of the charging switch and the calculated normal state both-end voltage difference of the charging switch, and diagnose whether the state of the discharging switch is the open stuck state based on the comparison result of the both-end voltage difference of the discharging switch and the calculated normal state both-end voltage difference of the discharging switch. calculate a normal state both-end voltage difference of the charging switch and a normal state both-end voltage difference of the discharging switch based on current information of the diagnosis power output by the diagnosis power unit and previously stored turn-on state resistance of each of the charging switch and the discharging switch, diagnose whether the state of the charging switch is the open stuck state based on the comparison result of the both-end voltage difference of the charging switch and the calculated normal state both-end voltage difference of the charging switch, and diagnose whether the state of the discharging switch is the open stuck state based on the comparison result of the both-end voltage difference of the discharging switch and the calculated normal state both-end voltage difference of the discharging switch.