A battery connection detection circuit is disclosed that is able to correctly determine an operation condition of a secondary battery and a connection condition between the secondary battery and a charging device. A determination circuit monitors both the voltage Vt1 on the battery connection terminal T1 and the current supplied to the secondary battery BAT, and therefore, the determination circuit can correctly determine the operation condition of the secondary battery and the connection condition between the secondary battery and the charging device even when high frequency noise is superposed on the power supply voltage Vdd, and when the power supply voltage decreases.