POWER STORAGE DEVICE AND VEHICLE-MOUNTED STRUCTURE THEREOF

A power storage device includes: a first case (100) that accommodates a plurality of stacked first power storage cells (10A); and a second case (200) that accommodates a plurality of stacked second power storage cells (10B). The first case (100) has a first reinforcement portion (120, 30A) extending in a first direction, and the second case (200) has a second reinforcement portion (220, 30B) extending in a second direction intersecting the first direction. The first case (100) and the second case (200) are provided to overlap with each other along a third direction intersecting the first direction and the second direction, and are joined to each other.