The battery charger is provided with temperature detection sections 12 to contact and detect the temperature of AA batteries 2A and AAA batteries 2B loaded in a battery pocket 3, and a charging circuit to detect battery temperature and control battery 2 charging. The battery charger is provided with AA battery 2A holders 11, which are circular openings 13 in the case 1, and AAA battery 2B holders 11, which are flexible arches 14. An AAA battery 2B is inserted into a flexible arch 14 and retained in a fixed position in the battery pocket 3. An AA battery 2A is not inserted into a flexible arch 14, but rather moves the flexible arch 14 causing it to incline, and is inserted into a circular opening 13 for retention in a fixed position in the battery pocket 3. The battery charger charges batteries 2 set in fixed positions in the battery pocket 3 while detecting battery 2 temperature via the temperature detection sections 12.