When starting charging of an internal battery as a result of connection of an external power source by an AC adapter, a charging control unit sets a first charging voltage at which the charging capacity of the internal battery is maximized. When starting the charging from recognition of reduced capacity of the internal battery due to its self-discharge in desk-top use where the AC adapter is in connection at all times, the charging control unit sets a second charging voltage lower than the first charging voltage to prevent the battery from degrading.