The invention provides an electrochemical device which is capable of quickly and surely eliminating a phenomenon of electrolyte solution decrease in a portion of a separation sheet, said portion being sandwiched between two electrode sheets, even if the phenomenon occurs frequently. An electrochemical device (100) is provided with an electricity storage element (13) that is configured of a first electrode sheet (13a), a second electrode sheet (13b) and a separation sheet (131c) that is interposed between the electrode sheets (13a, 13b). The separation sheet (131c) comprises: a first portion (a high liquid absorption part) (13c1) that is sandwiched between the electrode sheets (13a, 13b); a second portion (a low liquid absorption part) (13c2) that protrudes from the electrode sheets (13a, 13b), while being out of contact with a lid (12); and a third portion (a contact part) (13c3) that is in contact with an edge surface (13b3) of the second electrode sheet (13b).