Disclosed herein is a battery pack including: a plurality of cylindrical battery cells arranged in a plurality of rows and a plurality of layers; and a partition member for partitioning the battery cells; wherein each the battery cell is larger in diametral size on the positive electrode terminal side than on the negative electrode terminal side; the partition member includes a partition plate, and ribs formed in corners formed between the partition plate and support plates provided to be substantially orthogonal to the partition plate at substantially regular intervals, the ribs being operative to support the battery cells; and the ribs are formed correspondingly to the shape of the battery cell.