BATTERY PACK INCLUDING BATTERY MODULE

Disclosed is a battery pack having improved manufacturing efficiency, high energy density and enhanced product stability. The battery pack includes: a mounting structure including a first frame having a body portion with a plate and sidewalls bent from both ends of the body portion and extending upward to form an inner space above the plate, and a second frame coupled to a lower portion of the first frame and having a body portion with a plate and sidewalls bent from both ends of the body portion and extending downward to form an inner space below the plate; and at least two battery modules respectively accommodated in the inner spaces of the first frame and the second frame and including a plurality of cylindrical battery cells and a module case having a plurality of hollow tubes into which the plurality of cylindrical battery cells standing upright in an upper and lower direction are inserted and a connection portion configured to connect the plurality of hollow tubes to each other.