Disclosed herein is a battery pack that includes: a plurality of thin cells arranged in a matrix form in a first direction and a second direction perpendicular to the first direction, wherein a width of each thin cell in the first direction is smaller than widths of each thin cell in the second direction and a third direction perpendicular to the first and second directions, and wherein each of the thin cells has a surface substantially perpendicular to the first direction; a heat insulating member that insulates heat between the thin cells adjacent in the first direction; and a heat conducting member that contacts in common the surfaces of the thin cells arranged in the second direction.