BATTERY PACK

PROBLEM TO BE SOLVED: To provide a battery pack capable of enlarging a mounting area of a circuit board while preventing its size from increasing by reducing dead space on the circuit board.SOLUTION: A battery pack 10 comprises: a battery case 12; a circuit board 25 that is housed in the battery case 12 and on which circuit elements are mounted; and five cylindrical battery cells 20 housed substantially in a manner of log pile in the battery case 12. Three battery cells 20(1), 20(3), and 20(5) are located adjacent to a surface of the circuit board 25, the surface on which the circuit elements 27 are mounted. Of the three battery cells, the battery cell 20(3), which is located in the center between the battery cells 20(1) and 20(5) that are located on both sides, is displaced in the direction that moves away from the circuit board 25 with the displacement distance being less than the radius of the battery cell 20.