A power storage device which can have an improved performance such as higher discharge capacity and in which deterioration due to peeling of an active material layer or the like is difficult to occur, and a method for manufacturing the power storage device are provided. The power storage device includes a current collector, a mixed layer formed over the current collector, and a crystalline silicon layer which is formed over the mixed layer and functions as an active material layer. The crystalline silicon layer includes a crystalline silicon region and a whisker-like crystalline silicon region including a plurality of protrusions projecting over the crystalline silicon region. The whisker-like crystalline silicon region includes a protrusion having a bending or branching portion.