An electricity storage device (1) which is provided with an electricity storage element (40) and an outer case (10). This electricity storage device (1) is also provided with: a measurement substrate (81) which is connected to the electricity storage element (40), and through which a first electric current passes; and a main circuit substrate (82) through which a second electric current that is larger than the first electric current passes. The main circuit substrate (82) is arranged so as to face a part of a container (410) of the electricity storage element (40), said part being different from a long lateral surface (411) of the container (410).