To provide an electrochemical device which reliably overcoming disadvantages such as deterioration in dielectric strength and shortening of the life of a capacitor element as a whole. The capacitor element 10 has a form in which a laminate formed by superposition of a first electrode sheet 11, a separation sheet 14, a second electrode sheet 12, a separation sheet 14, and a third electrode sheet 13 in the named order from the bottom, is folded along a prescribed line VSL. In the form, the current-collecting electrode layer 11a and polarizable electrode layer 11b of the first electrode sheet 11, the current-collecting electrode layer 12a and polarizable electrode layer 12b of the second electrode sheet 12, the current-collecting electrode 13a and polarizable electrode layer 13b of the third electrode sheet 13, and the two separation sheets 14 are each kept continuous through the folding position.