A thin battery and a monolithic thin battery, wherein in an anode collector plate (3) and in a cathode collector plate (4) left are parts (31, 41) not provided with active materials, electrolytes and sealing agents (2a, 2b). On one side of each of the collector plates (3, 4), provided are terminal pieces (53, 54). Since the parts (31, 41) function as heat dissipating fins, excellent heat dissipation can be performed.