A first secondary battery cell and a second secondary battery cell each having a cylindrical shape and connected in series and/or in parallel with each other are aligned and housed in such postures that side surfaces of the cylindrical shapes face each other. A battery pack includes: a longitudinal partition plate disposed at an interface between the first secondary battery cell and the second secondary battery cell housed in an internal space of a housing case; a lead plate that crosses the longitudinal partition plate; and a lateral partition plate that covers the end surfaces of the first secondary battery cell and the second secondary battery cell. The lateral partition plate and the lead plate pass through a longitudinal side slit in a state of overlap between the lateral partition plate and the lead plate.