A charging system is configured to charge a battery pack including one or more battery cells. The charging system includes an acquirer and a controller. The acquirer is configured to acquire, as an acquisition voltage, a voltage between terminals or a cell voltage of each of the one or more battery cells in the battery pack which is being charged. The controller is configured to, when the voltage between the terminals or the cell voltage reaches a target voltage, cause a first charging mode allowing fast charging to transition to a second charging mode in which a charge current is lower than in the first charging mode. The controller is configured to stop charging operation when the acquisition voltage acquired by the acquirer decreases and an aspect of a decrease in the acquisition voltage satisfies a predetermined condition in the second charging mode.