To provide a charger excellent in safety by preventing the erroneous mounting of a battery, and a charging method.

A charge control circuit 30 gets a voltage value V23 measured by a voltage measuring circuit 20 and performs switching between a charge circuit 10 and a charge terminal 42 for a cathode based on it. To be concrete, the charge control circuit 30 closes a line between the charge terminal 42 for a cathode and the charge circuit 10 in the case that the the voltage value V23 measured by the voltage measuring circuit 20 is 0(V), and keeps an open condition in the case that the voltage value V23 is larger than 0(V).