To provide a battery pack improving protection of an outer packaging portion against external force.

The battery pack 1 in which a protection circuit 16 is mounted on a unit cell 2 includes a first frame 13 supporting the protection circuit 16 and a second metallic frame 10 supporting the first frame 13, the first frame 13 is engaged with the second fame 10, and the second frame 10 is fixed to the unit cell 2. Thereby, the deformation and the position movement of the first frame 13 caused by external force is suppressed by means of the second frame 10, and breakage of various kinds of component or a joining part can be prevented.