The invention relates to a battery pack capable of reducing a circuit board and at the same time reducing the shape by separating the parts susceptible to heat from a heat-emitting current detection resistor. A battery pack includes a battery block 10 including plural batteries 1 accommodated in a battery accommodating portion 15 of a battery holder 2, and a current detecting resistor 40 detecting the currents of the batteries 1. The holder 2 includes a pair of support side walls 12 arranged on both sides of the accommodating portion 15. The pair of side walls 12 have electrode windows 19 opening to connect lead plates 5 to end electrodes of the batteries 1 that are accommodated in the accommodating portion 15. The lead plates 5 are arranged on the exterior sides of the side walls 12. The side walls 12 are formed wider than the accommodating portion 15 to form protruding portions 16 protruding externally from the accommodating portion 15. The current detecting resistor 40 is arranged on the interior sides of the protruding portions 16 of the pair of side walls 12.