Disclosed is a serial-to-parallel converting apparatus. The serial-to-parallel converting apparatus includes: an input plate connected to positive electrodes and negative electrodes of a plurality of battery cells, respectively: an output plate spaced apart from the input plate and connected to an external terminal; a rotary plate rotatably interposed between the input plate and the output plate to electrically connect the input plate and the output plate, the rotary plate being configured to convert serial connection and parallel connection of the plurality of battery cells by rotating; and a case configured to accommodate the input plate, the output plate and the rotary plate.