A battery pack (1, 3, 5) comprising: a first battery module (2A, 4A, 6A) and a second battery module (2B, 4B, 6B) that are arranged adjacent to each other so as to define an open space portion, each of the battery modules (2A, 2B, 4A, 4B, 6A, 6B) having a case (90A, 90B, 190A, 190B, 290A, 290B) for housing at least one single cell (10A-10D), wherein a wall portion (91A, 91B, 191A, 191B, 291) of each case (90A, 90B, 190A, 190B, 290A, 290B) comprises: a vent (92A, 92B, 192A, 192B, 292A, 292B) including a cut-out in the wall portion (91A, 91B, 191A, 191B, 291) through which an inside and an outside of the case (90A, 90B, 190A, 190B, 290A, 290B) communicate with each other during normal operation of the battery module (2A, 2B, 4A, 4B, 6A, 6B), and a wall region (93A, 93B, 193A, 193B, 293) where the vent (92A, 92B, 192A, 192B, 292A, 292B) is not provided, characterized in that the vent (92A, 192A, 292A) provided on the case of the first battery module (2A, 4A, 6A) is open toward the open space portion, and faces the wall region (93B, 193B, 293) provided on the case (90B, 190B, 290B) of the second battery module (2B, 4B, 6B), which is adjacent to the first battery module (2A, 4A, 6A), such that the vent (92A, 192A, 292A) provided on the case (90A, 190A, 290A) of the first battery module (2A, 4A, 6A) does not face a vent (92B, 192B, 292B) provided on the case (90B, 190B, 290B) of the second battery module (2B, 4B, 6B). a first battery module (2A, 4A, 6A) and a second battery module (2B, 4B, 6B) that are arranged adjacent to each other so as to define an open space portion, each of the battery modules (2A, 2B, 4A, 4B, 6A, 6B) having a case (90A, 90B, 190A, 190B, 290A, 290B) for housing at least one single cell (10A-10D), wherein a wall portion (91A, 91B, 191A, 191B, 291) of each case (90A, 90B, 190A, 190B, 290A, 290B) comprises: a vent (92A, 92B, 192A, 192B, 292A, 292B) including a cut-out in the wall portion (91A, 91B, 191A, 191B, 291) through which an inside and an outside of the case (90A, 90B, 190A, 190B, 290A, 290B) communicate with each other during normal operation of the battery module (2A, 2B, 4A, 4B, 6A, 6B), and a wall region (93A, 93B, 193A, 193B, 293) where the vent (92A, 92B, 192A, 192B, 292A, 292B) is not provided, a vent (92A, 92B, 192A, 192B, 292A, 292B) including a cut-out in the wall portion (91A, 91B, 191A, 191B, 291) through which an inside and an outside of the case (90A, 90B, 190A, 190B, 290A, 290B) communicate with each other during normal operation of the battery module (2A, 2B, 4A, 4B, 6A, 6B), and a wall region (93A, 93B, 193A, 193B, 293) where the vent (92A, 92B, 192A, 192B, 292A, 292B) is not provided, characterized in that the vent (92A, 192A, 292A) provided on the case of the first battery module (2A, 4A, 6A) is open toward the open space portion, and faces the wall region (93B, 193B, 293) provided on the case (90B, 190B, 290B) of the second battery module (2B, 4B, 6B), which is adjacent to the first battery module (2A, 4A, 6A), such that the vent (92A, 192A, 292A) provided on the case (90A, 190A, 290A) of the first battery module (2A, 4A, 6A) does not face a vent (92B, 192B, 292B) provided on the case (90B, 190B, 290B) of the second battery module (2B, 4B, 6B).