Structure of thin battery, battery pack, and method for manufacturing battery pack

To provide a thinner, lighter battery pack and to reduce the cost by eliminating the need for a battery case. A thin battery pack structure using an outer packaging film (battery pack) is constructed by a flat and rectangular shaped battery cell, a flat and rectangular shaped frame portion accommodating the battery cell, a circuit board unit disposed on the outer side surface of the frame portion, a cap portion mounted on one end of the frame portion and the battery cell so as to sandwich the circuit board unit with the outer side surface of the frame portion, and an outer packaging film for integrally covering the rectangular battery cell and the frame portion.