A flexible printed circuit board which includes: a base film; and multiple wires formed on the base film, in which in a region attached to a battery including multiple arrayed cells, a conductor portion to be the multiple wires is provided only on one surface of the base film, at at least part of a region apart from the region attached to the battery, a conductor portion to be the multiple wires is provided on each surface of the base film, and the flexible printed circuit board further includes multiple conductive portions configured to electrically connect the wires on one surface side of the base film and the wires on the other surface side of the base film.