To reduce difference in temperature among batteries, while attaining low cost mass production, and to reduce the difference in temperatures among power sources by using a battery holder having many batteries arranged in multiple stages and multiple columns.

A battery pack includes a plurality of chargeable batteries 1 and the battery holder 2, configured by arranging the respective batteries 1 in multiple stages and multiple columns in a parallel posture. In the battery holder 2, an insertion part 21 into which the battery 1 is inserted and disposed at a fixed position is provided being partitioned by a barrier wall 22 and each battery 1 is in contact with the barrier wall 22 in a thermal-coupled state to conduct heat generated from the battery 1 to the battery holder 2 to radiate heat. In the battery holder 2, a surface portion of the barrier wall 22 is made thicker than its center part, such that the heat capacity of the barrier wall 22 which is thermal-coupled with the batteries 1 disposed at the center part of the battery holder 2 is made larger than the heat capacity of the barrier wall 22 which is thermally coupled with the batteries 1 disposed on a surface part of the battery holder 2.