An electrochemical device includes four or more electrodes which are laminated with separators provided between the respective electrodes, an electrolyte filled between the respective electrodes, and a sealing member which covers the periphery. The electrodes are arranged so that the polarities alternately change in the lamination direction, and each of the electrodes has projections projecting from diagonally opposite positions on the peripheral edge so that the positions of the projections of the electrodes of different polarities are opposite to each other in the lateral direction and the projections of the electrodes of the same polarity are aligned and connected with each other.