A battery module comprising: a plurality of battery cells stacked in a first direction; a duct through which gas discharged from each of the battery cells flows, the duct extending in the first direction with the duct facing the plurality of battery cells in a second direction orthogonal to the first direction; and an attachment-target member to which the duct is attached, the attachment-target member being held by the battery cells, wherein the attachment-target member has a pair of first wall portions facing each other with a space being interposed between the pair of first wall portions in a third direction orthogonal to the first direction and the second direction, the duct has a pair of second wall portions respectively facing the pair of first wall portions in the third direction, and is disposed between the pair of first wall portions, characterized in that one wall portion that is one of each first wall portion and each second wall portion is provided with a claw portion having a protruding shape protruding in the third direction, the other wall portion that is the other of each first wall portion and each second wall portion is provided with a groove portion having a recessed shape recessed in the third direction, and the groove portion includes a first segment portion and a second segment portion, the first segment portion extending in the first direction, the claw portion being disposed in the first segment portion, the first segment portion anchoring the claw portion in the second direction, the second segment portion being opened at an end portion of the other wall portion in the second direction, the second segment portion extending in a direction intersecting the first direction, the second segment portion being connected to the first segment portion, the second segment portion allowing the claw portion to enter the first segment portion when attaching the duct to the attachment-target member. a plurality of battery cells stacked in a first direction; a duct through which gas discharged from each of the battery cells flows, the duct extending in the first direction with the duct facing the plurality of battery cells in a second direction orthogonal to the first direction; and an attachment-target member to which the duct is attached, the attachment-target member being held by the battery cells, wherein the attachment-target member has a pair of first wall portions facing each other with a space being interposed between the pair of first wall portions in a third direction orthogonal to the first direction and the second direction, the duct has a pair of second wall portions respectively facing the pair of first wall portions in the third direction, and is disposed between the pair of first wall portions, characterized in that one wall portion that is one of each first wall portion and each second wall portion is provided with a claw portion having a protruding shape protruding in the third direction, the other wall portion that is the other of each first wall portion and each second wall portion is provided with a groove portion having a recessed shape recessed in the third direction, and the groove portion includes a first segment portion and a second segment portion, the first segment portion extending in the first direction, the claw portion being disposed in the first segment portion, the first segment portion anchoring the claw portion in the second direction, the second segment portion being opened at an end portion of the other wall portion in the second direction, the second segment portion extending in a direction intersecting the first direction, the second segment portion being connected to the first segment portion, the second segment portion allowing the claw portion to enter the first segment portion when attaching the duct to the attachment-target member.