An in-vehicle battery module includes a plurality of cylindrical battery cells, a battery cell holder, a protective case, a vent cover provided such that the battery cell holder is positioned between the protective case and the vent cover, the vent cover and the battery cell holder disposed such that a vent space in which gas discharged from an end face on a second-electrode side of the cylindrical battery cell flows is provided between the vent cover and the battery cell holder, at least one first-electrode bus bar, at least one second-electrode bus bar provided in the vent space, and a support member disposed partially in the vent space and the support member being configured to support the second-electrode bus bar from the vent cover side.