To efficiently emit light of a light emitting diode to the outside by a lamp reader while facilitating assembly.

The back battery includes a case 1, a battery 2 incorporated in the case 1, a circuit board 3 connected to the battery 2, a light emitting diode 4 made to emit light by an electronic circuit to be mounted on the circuit board 3, and the translucent lamp reader 5 which guides the light of the light emitting diode 4 to outside the case 1. The circuit board 3 has a first circuit board 3A and a second circuit board 3B. The first circuit board 3A and the second circuit board 3B are disposed at fixed position with a separator 6 clamped. The separator 6 and the lamp reader 5 are molded in one body of a translucent material such as plastic or glass having light transparency.

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