A power storage device 1 comprises: a power storage module 3; a current collector plate 5 stacked on the power storage module 3; an insulating plate 20A, 20B stacked on the current collector plate 5; and an arresting plate 8 stacked on the insulating plate 20A, 20B. The insulating plate 20A, 20B and the arresting plate 8 have mutually different coefficients of thermal expansion. The insulating plate 20A, 20B includes an opposing surface 20a opposing the arresting plate 8, and a projecting portion 30 provided in a position spaced apart from the center of the opposing surface 20a. The arresting plate 8 has a hole 40 into which the projecting portion 30 is inserted. The projecting portion 30 is divided into a first projection 31 and a second projection 32 in a second direction D2 intersecting the first direction D1. The first projection 31 is disposed towards the center of the opposing surface 20a in the second direction D2. The second projection 32 is disposed towards the outer edge of the opposing surface 20a in the second direction D2.