In a battery pack including a battery case containing therein a battery cell, a wiring circuit board, and a liquid-absorbing element capable of absorbing the electrolyte leaking out from the battery cell, the liquid-absorbing element is inserted with looseness allowing for expansion in a gap formed by a retaining element on the inner wall surface of the battery case or retaining element on the wiring circuit board. Alternatively, a liquid-absorbing element consisting of a non-absorbent porous retaining element partially holding a liquid absorbent is used and the porous retaining element is fixed to the inner wall surface of the battery case or the wiring circuit board at an absorbent-free zone.