A duct holding structure for a battery assembly body comprises: insulating resin bus bar modules (11a, 11b) attached to a battery assembly body (2) in which a plurality of batteries (1) are arranged and connected in series and holding a bus bar (9) for connecting between the electrodes of adjacent batteries (1); and an insulating resin duct (3) attached to the battery assembly body (2) while covering a degassing opening formed on an electrode surface (6) from which an electrode of each of the batteries (1) projects. In the duct holding structure, the duct (3) and the bus bar modules (11a, 11b) are provided with a locking mechanism (23) by which the duct (3) is locked to the bus bar modules (11a, 11b).