The present invention provides an electric storage device with a reduced size. A monocell (an example of the electric storage device) (14) comprises an electric power generation element (50) and an outer case (62) for accommodating the electric power generation element (50) and having an inner wall (62A) with a recess (64) in a portion thereof opposite to a convex portion at a lower end of the electric power generation element (50). Therefore, compared with the conventional outer case (62) without the recess (64), even when the outer case (62) is arranged close to the electric power generation element (50), a predetermined clearance (CL) can be provided, thereby reducing the size of the monocell (14). Furthermore, because the recess is formed in the inner wall (62A) of the outer case (62), the surface area of the inner wall (62A) can be increased. With this configuration, efficiency in cooling of the monocell (14) can be improved.