To provide a power storage device having excellent charge/discharge cycle characteristics and a high charge/discharge capacity. The following electrode is used as an electrode of a power storage device: an electrode including a current collector and an active material layer provided over the current collector. The active material layer includes a plurality of whisker-like active material bodies. Each of the plurality of whisker-like active material bodies includes at least a core and an outer shell provided to cover the core. The outer shell is amorphous, and a portion between the current collector and the core of the active material bodies is amorphous. Note that a metal layer may be provided instead of the current collector, the active material bodies do not necessarily have to include the core, and a mixed layer may be provided between the current collector and the active material layer.