An electrochemical device is disclosed. The device comprises a casing having a recess with an opening on a top face of the recess, a lid configured to block the recess of the casing so that the recess is watertight and airtight, a rechargeable and dischargeable storage element and an electrolytic solution enclosed in the recess, and a separate sheet interposed between the first and second electrode sheets, the separate sheet having a higher liquid absorption section interposed between the first and second electrode sheets, and a lower liquid absorption section continuously connected to the higher liquid absorption section, having a liquid absorption smaller than that of the higher liquid absorption section and extending outwardly with respect to the first and second electrode sheets. The lower liquid absorption section has a thickness greater than that of the higher liquid absorption section.