Disclosed is an electricity storage device which can be charged/discharged at high rate 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 disposed on the positive electrode collector and including a positive electrode active material which can reversibly absorb/desorb at least anions; a negative electrode collector; and a negative electrode disposed on the negative electrode collector and including a 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, a silicon-containing alloy, a silicon compound, tin, a tin-containing alloy, and a tin compound; and the negative electrode is formed as a thin film having a thickness of 10 µm or less.