Disclosed is a balancing apparatus capable of performing balancing without wasting power and of rapidly transmitting power. A battery stack balancing apparatus for balancing a battery stack including a plurality of battery modules connected to each other in series includes a series resonant circuit including a first capacitor and a first inductor connected to the first capacitor in series, a polarity change circuit including a second inductor and a polarity change switch connected to the second inductor in series so as to be selectively turned on or off, and connected to the first capacitor in parallel, a plurality of transmission lines having ends, respectively, electrically connected to a plurality of nodes provided at a low-potential end of the battery stack, at a high-potential end of the battery stack, and between the plurality of battery modules connected to each other in series, and other ends connected to the series resonant circuit, a plurality of transmission switches provided on the plurality of transmission lines so as to be selectively turned on or off, and a control unit configured to control the plurality of transmission switches and the polarity change switch.