PURPOSE: To provide a charger which can surely avoid the drop of the insulating performance of a transformer, the deformation of a charger case by high temperature, etc.

CONSTITUTION: The voltage from a power source is lowered to the specified voltage with a transformer 4 after passing a circuit 2 on power source side, and is taken in a charge control circuit 8. The charge control circuit 8 applies the voltage lowered by the transformer 4 to a battery 10 so as to perform the charge. The transformer 4 is provided with a transformer temperature detecting circuit 6, which detects the temperature of the transformer 4. In case that the temperature of the transformer 4 reaches the temperature regulation value set in RAM26, CPU 20 lowers the charge current value from, for example, 2A to 1.5A so as to avoid the drop of insulation performance of the transformer 4, the transformation of an outer case, etc.