INTERNAL RESISTANCE DETECTION DEVICE AND POWER SOURCE DEVICE

Provided is a configuration that can detect the internal resistance of a power storage unit. An internal resistance detection device includes a DC-DC converter that is configured to raise the output voltage to a target voltage by performing constant current operation in which the charging current is output at a target charging current, and, when the output voltage reaches the target voltage, to control power such that the charging current is lowered by performing constant voltage operation in which the output voltage is fixed at the target voltage. A control unit detects the internal resistance of a power storage unit based on a target charging current Ichg during constant current operation by the DC-DC converter, a drop time, which is the time that passes from when constant voltage operation starts to when the charging current drops to a predetermined current value, and a capacity of the power storage unit.