Provided is an electrochemical device which is capable of suppressing problems affecting the capacitor element as a whole, such as a drop in its voltage resistance characteristics and shortening of its life. The capacitor element (10) is constituted of 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, and folding the laminate along a reference line VSL to double the laminate. In the resulting folded laminate, a collector electrode layer (11a) and polarizable electrode layer (11b) of the first electrode sheet (11), the collector electrode layer (12a) and polarizable electrode layer (12b) of the second electrode sheet (12), the collector electrode (13a) and polarizable electrode layer (13b) of the third electrode sheet (13), and the two separation sheets (14) are connected to each other at the respective folded locations.