voltage vbatt is extracted from the connection point of the fet f 1 and the fet f 2 connected in series and the battery voltage vbatt is then supplied to the controller 11 the led 13 indicating the state of charging is connected to the controller 11 the charging control by the controller 11 will be explained referring to a flowchart shown in fig5 upon detecting attachment of the secondary battery bat by the switch sw the detection signal batt goes l whereby the charging operation starts in step s 1 the drive signal dr 1 goes h to thereby turn fet f 1 off the drive signal dr 2 goes l to thereby turn the fet f 2 on and the drive signal dr 3 goes l to thereby turn the transistor tr 1 on as a consequence the secondary battery bat is initially charged through the transistor tr 1 a resistor r 10 and the fet f 2 in the initial charging mode the led 13 kept turned off in the standby mode illuminates the initial charging current if is expressed by the equation 1 below in the equation 1 vtr represents emitter collector voltage of the transistor tr 1 in step s.