In an electrochemical device comprising a multilayer body having a separator and a pair of electrodes disposed so as to hold the separator therebetween, and an electrolyte infiltrated in the multilayer body; the electrodes contain an active material particle; the separator is made of a nonwoven fabric having an average fiber diameter Df of 0.1 to 1.0 μm; T≧5 μm and T/Df≧20, where T is the thickness of the separator; and Dp