A power source apparatus including batteries having positive and negative electrode regions, parallel blocks with batteries stacked together and electrically connected in parallel, multiple parallel-series connected blocks with the parallel blocks electrically connected in series, and bus-bars having a plurality of terminal insertion holes. Batteries in a parallel block are stacked together lining-up positive electrode regions on one side and negative electrode regions on the other side. Parallel blocks in a multiple parallel-series connected block are stacked so as to reverse the orientation of each block added to the stack. The bus-bars are integrated pieces that can electrically connect the batteries in a parallel block in parallel as well as electrically connect the parallel blocks in series.