A battery pack that is mounted to a laptop computer, wherein two or more battery cells that can be charged and discharged are housed in a pack case; the battery cells are cylindrical battery cells having a circular vertical cross-section; the pack case is configured with a lower case in which battery cells are received and an upper case that is coupled to the lower case in order to close and seal the battery cells; in the upper case, a thickness of an upper contact point portion that contacts an upper end external circumferential surface of the battery cells is 70% or less of that of the remaining portions of the upper case, and a first sheet is attached to an outer surface of the upper case corresponding to the upper contact point portion; and in the lower case, a thickness of a lower contact point portion that contacts a lower end external circumferential surface of the battery cells is 70% or less of that of the remaining portions of the lower case, and a second sheet is attached to an outer surface of the lower case corresponding to the lower contact point portion.