A battery pack includes a first battery module and a second battery module arranged adjacent the first battery module so as to define an open space portion. Each of the first and second battery modules includes a case configured to house at least one single cell. Each case includes a wall portion including a vent through which an inside of the case is capable of communicating with an area outside the case, and a wall region without the vent. The vent disposed in the wall portion of the case of the first battery module opens toward the open space portion and toward the wall region of the case of the second battery module, when the first battery module is disposed adjacent to the second battery module.