An electrochemical device comprises an element body 10 in which a pair of a first inner electrode and a second inner electrode are laminated to sandwich a separator layer; an exterior sheet 4 covering the element body; a first lead terminal 18 drawn to an outside of the exterior sheet 4; and a second lead terminal 28 drawn to the outside of the exterior sheet 4. A proof stress of the exterior sheet is 390 to 980 N/mm2 in JIS Z2241, and a hardness of the exterior sheet is 230 to 380 Hv in Vickers hardness (JIS Z2244).