NOVELTY - The power storage device comprises a positive electrode (202) in which a positive electrode active material is formed over a positive electrode current collector (200), and a negative electrode (207) that faces the positive electrode with an electrolyte interposed between the negative electrode and the positive electrode. The positive electrode active material comprises a film-form first region including phosphate compound having a region having an olivine structure, and a film-form second region including phosphate compound having a region having an olivine structure.    USE - The power storage device such as lithium-ion secondary battery is useful: for portable electronic devices such as personal computers, cellular phones or cellular phone devices, digital cameras or video cameras, digital photo frames, portable game machines, portable information terminals, audio reproducing devices and display devices; in electric propulsion vehicles such as electric vehicles, hybrid vehicles, train vehicles, maintenance vehicles, carts, wheelchairs and bicycles; and in a wireless power feeding system such as an radio frequency power feeding system.    ADVANTAGE - The power storage device can be easily and economically manufactured with reduced size, lightweight, high reliability, improved discharge voltage capacity and energy density and increased power storage capacity and without deterioration or breakdown.    DETAILED DESCRIPTION - The power storage device comprises a positive electrode (202) in which a positive electrode active material is formed over a positive electrode current collector (200), and a negative electrode (207) that faces the positive electrode with an electrolyte interposed between the negative electrode and the positive electrode. The positive electrode active material comprises a film-form first region including phosphate compound having a region having an olivine structure, and a film-form second region including phosphate compound having a region having an olivine structure. Top surfaces, side surfaces, and bottom surfaces of the film-form first region are covered with the film-form second region.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a power storage device.    Positive electrode current collector (200)    Positive electrode active material layer (201)    Positive electrode (202)    Negative electrode current collector (205)    Negative electrode active material layer (206)    Negative electrode. (207)