A battery pack includes a first unit battery, a second unit battery, and a spacer. The first unit battery includes a wound electrode body and a casing that accommodates an electrolyte solution. The spacer includes: a primary surface that faces the first unit battery; and plural projections, each of which is projected from the primary surface. The plural projections include: a first projection that abuts the casing in a state where the casing is not expanded; and a second projection, a height of which is lower than a height of the first projection.