Disclosed herein is a battery cell voltage balancing device for connecting two or more battery cells to one another in parallel so as to minimize a voltage difference between the respective battery cells, the battery cell voltage balancing device including an insulative main body having partitions, between which the two or more battery cells are mounted, respectively, configured in a structure in which the partitions are open upward, terminal connection parts disposed at opposite ends of the insulative main body for connecting cathodes and anodes of the battery cells mounted at the insulative main body to cathodes and anodes of neighboring battery cells mounted at the insulative main body, and an interval adjustment unit for variably adjusting an interval between the partitions in a state in which the battery cells are mounted between the partitions to achieve secure mounting of the battery cells between the respective partitions and electrical connection of electrode terminals of the respective battery cells to the terminal connection parts.