NOVELTY - The power storage device has a current collector, a silicon layer having a function as an active material layer over the current collector. The silicon layer comprises a thin film portion in contact with the current collector, bases, and a whisker-like protrusions extending from base. The whisker-like protrusion extended from base, is in contact with a whisker-like protrusion extending from another base. The thin film portion comprises amorphous silicon, while the whisker-like protrusion comprises a core formed using crystalline silicon.    USE - Power storage device for use in electric devices. Can also be used in moving objects, electric vehicles, hybrid vehicles which include both an internal-combustion engine and an electric motor, motorized bicycles including motor-assisted bicycles, display devices, lighting devices, desktop personal computers and laptop personal computers, image reproduction devices, mobile phones, portable game machines, portable information terminals, e-book readers, cameras such as video cameras and digital still cameras, high-frequency heating devices such as microwave ovens, electric rice cookers, electric washing machines, air-conditioning systems such as air conditioners, electric refrigerators, electric freezers, electric refrigerator-freezers, freezers for preserving DNA, and medical electrical equipment such as dialyzers.    ADVANTAGE - Improves the mechanical strength of a whisker since the whisker has a diameter large enough to maintain its strength. Prevents distortion due to expansion from being concentrated on one point, thus suppressing the breakage of the whisker. Prevents the tripping of a circuit breaker of a commercial power supply in use of electric devices by using the power storage device as an auxiliary power supply for supplying power which cannot be supplied enough by a commercial power supply.    DESCRIPTION OF DRAWING(S) - The drawing shows the image of the cross-section of whisker.    Cross-section of whisker (600)