A charging device comprising: a charging power circuit adapted to supply a charging electric power to a battery; a pair of input power terminals (11, 12) to be connected to an AC power source; a constant voltage power circuit adapted to supply a DC voltage (Vcc); a pair of output lines (L1, L2) adapted to supply a charging voltage by connecting the anode and cathode terminals (O1, O2) of the battery to be charged between the pair of output lines (L1, L2); a component circuit part of the charging device connected by traversing a part between the pair of output lines (L1, L2); and a discharge preventing circuit comprising a first switching element connected between the component circuit part and one of the output lines (L1, L2), wherein the first switching element has an off state adapted to interrupt a discharging path to the battery formed by the component circuit, characterised in that the discharge preventing circuit further comprises a second switching element which is connected between the pair of output lines (L1, L2) in parallel to the battery adapted to control the on/off state of the first switching element as follows: during an ordinary charging operation in which the input power terminals (11, 12) are connected to the AC power source, the constant voltage power circuit supplies the DC voltage (Vcc) to a voltage dividing circuit composed of two series resistances (125, 126), wherein a voltage dividing point of the two series resistances (125, 126) is connected to the gate of the second switching element so that the second switching element is biased to a turned on state by the DC voltage (Vcc) thereby controlling the first switching element to an on state; and in a state in which the input power terminals (I1, I2) are not connected to the AC power source, the constant voltage power circuit does not output the DC voltage (Vcc), so that no voltage is applied to the series resistances (125, 126) and the second switching element is in a turned off state thereby controlling the first switching element to the off state interrupting the discharging path to the battery formed by the component circuit. a charging power circuit adapted to supply a charging electric power to a battery; a pair of input power terminals (11, 12) to be connected to an AC power source; a constant voltage power circuit adapted to supply a DC voltage (Vcc); a pair of output lines (L1, L2) adapted to supply a charging voltage by connecting the anode and cathode terminals (O1, O2) of the battery to be charged between the pair of output lines (L1, L2); a component circuit part of the charging device connected by traversing a part between the pair of output lines (L1, L2); and a discharge preventing circuit comprising a first switching element connected between the component circuit part and one of the output lines (L1, L2), wherein the first switching element has an off state adapted to interrupt a discharging path to the battery formed by the component circuit, characterised in that the discharge preventing circuit further comprises a second switching element which is connected between the pair of output lines (L1, L2) in parallel to the battery adapted to control the on/off state of the first switching element as follows: during an ordinary charging operation in which the input power terminals (11, 12) are connected to the AC power source, the constant voltage power circuit supplies the DC voltage (Vcc) to a voltage dividing circuit composed of two series resistances (125, 126), wherein a voltage dividing point of the two series resistances (125, 126) is connected to the gate of the second switching element so that the second switching element is biased to a turned on state by the DC voltage (Vcc) thereby controlling the first switching element to an on state; and in a state in which the input power terminals (I1, I2) are not connected to the AC power source, the constant voltage power circuit does not output the DC voltage (Vcc), so that no voltage is applied to the series resistances (125, 126) and the second switching element is in a turned off state thereby controlling the first switching element to the off state interrupting the discharging path to the battery formed by the component circuit. during an ordinary charging operation in which the input power terminals (11, 12) are connected to the AC power source, the constant voltage power circuit supplies the DC voltage (Vcc) to a voltage dividing circuit composed of two series resistances (125, 126), wherein a voltage dividing point of the two series resistances (125, 126) is connected to the gate of the second switching element so that the second switching element is biased to a turned on state by the DC voltage (Vcc) thereby controlling the first switching element to an on state; and in a state in which the input power terminals (I1, I2) are not connected to the AC power source, the constant voltage power circuit does not output the DC voltage (Vcc), so that no voltage is applied to the series resistances (125, 126) and the second switching element is in a turned off state thereby controlling the first switching element to the off state interrupting the discharging path to the battery formed by the component circuit.