To provide a charger which can charge both battery packs of a battery pack adaptable to cooling and a battery pack not adaptable to cooling with a precise charging current in accurate full charge control.

Based on the output of a battery temperature gradient calculating means by CPU 51 and a battery temperature gradient storage means 532, this charger discriminates the full charge of a battery pack 2 at a battery temperature gradient with a first sampling width set by a microcomputer 50, and judges the existence of the cooling effect by the gradient of the battery temperature with the second sampling with the width wider than the first sampling width set by the microcomputer 50, based on the battery temperature at start of charge detected by the battery temperature detecting means 90.