A power storage device includes a fuel cell (33), a battery holder (1) and an end plate (40) for sandwiching and binding the fuel cell, and an interposed member (11) disposed between the end plate (40) and the fuel cell (33). The battery holder (1) and the end plate (40) are made of resin, and have a positive coefficient of thermal expansion at a temperature lower than a predetermined temperature. The interposed member (11) is formed to have a substantially negative coefficient of thermal expansion at a temperature lower than the predetermined temperature.