A charging circuit, comprising: an input component into which power for charging a secondary battery is input; a charging control unit configured to be driven with power supplied from the input component to control a charging current that is applied to the secondary battery, the charging control unit being connected to a power line connecting the input component to the secondary battery; a main switching element configured to be turned on in a state where a potential difference between the input component and a gate terminal is higher than or equal to a set value, the main switching element being provided on the input component side of the power line relative to the charging control unit; a time constant circuit having a function of maintaining the potential difference at the set value or higher for a predetermined time after power is input to the input component and a function of maintaining the potential difference at lower than the set value after the predetermined time is elapsed; a control unit configured to be driven with power supplied from the input component to control the main switching element, the control unit being connected to the secondary battery side of the power line relative to the main switching element; and a full charge detector configured to detect a fully charged state of the secondary battery, wherein the control unit maintains an ON state of the main switching element by being driven within the predetermined time after power is input to the input component and stopping the function of the time constant circuit, and when the full charge detector detects the fully charged state, the control unit restarts the time constant circuit after the predetermined time is elapsed and after a set predetermined time is elapsed in the time constant circuit, the main switching element is turned off. an input component into which power for charging a secondary battery is input; a charging control unit configured to be driven with power supplied from the input component to control a charging current that is applied to the secondary battery, the charging control unit being connected to a power line connecting the input component to the secondary battery; a main switching element configured to be turned on in a state where a potential difference between the input component and a gate terminal is higher than or equal to a set value, the main switching element being provided on the input component side of the power line relative to the charging control unit; a time constant circuit having a function of maintaining the potential difference at the set value or higher for a predetermined time after power is input to the input component and a function of maintaining the potential difference at lower than the set value after the predetermined time is elapsed; a control unit configured to be driven with power supplied from the input component to control the main switching element, the control unit being connected to the secondary battery side of the power line relative to the main switching element; and a full charge detector configured to detect a fully charged state of the secondary battery, wherein the control unit maintains an ON state of the main switching element by being driven within the predetermined time after power is input to the input component and stopping the function of the time constant circuit, and when the full charge detector detects the fully charged state, the control unit restarts the time constant circuit after the predetermined time is elapsed and after a set predetermined time is elapsed in the time constant circuit, the main switching element is turned off.