A spacer includes: a first projection being in contact with the battery cell; a second projection being in contact with the battery cell; a third projection adjacent to the first projection, and being in contact with the battery cell; a first inclined portion connecting the first projection and the third projection; a fourth projection adjacent to the second projection, and being in contact with the battery cell; a second inclined portion connecting the second projection and the fourth projection; and a fifth projection and a sixth projection being out of contact with the battery cells between the third projection and the fourth projection. When the battery cells expand, the fifth and the sixth projections come into contact with the battery cells.