Disclosed is an electricity storage device which can be charged/discharged at high speed and have high output, high capacity and excellent repeating charge/discharge characteristics, although it uses a non-carbon material as a negative electrode active material. Specifically disclosed is an electricity storage device comprising a positive electrode collector, a positive electrode arranged on the positive electrode collector and containing a positive electrode active material which can reversibly absorb/desorb at least anions, a negative electrode collector, and a negative electrode arranged on the negative electrode collector and composed ofa negative electrode active material which can substantially absorb/desorb lithium ions reversibly. The negative electrode active material is composed of at least one substance selected from the group consisting of silicon, silicon-containing alloys, silicon compounds, tin, tin-containing alloys and tin compounds; and the negative electrode is formed as a thin film having a thickness of not more than 10 [mu]m.