The present invention relates to a system for detecting swelling of a battery, the system including: a plurality of detecting units which is provided at one or more battery modules of a battery pack, respectively, and detects gas branched from a battery cell of the battery module; a control unit which selects the largest detection value among the detection values of the respective detecting units, determines a level of the selected detection value according to a size of the selected detection value, and controls an operation of a peripheral apparatus based on the corresponding level; and a switch unit which is provided in a connection path of the battery pack and an external power source and is turned on and off according to a signal of the control unit.