A driving force transmission device with a dry clutch for selectively connecting and disconnecting a driving force disposed in a sealed space, the dry clutch comprising: - a first clutch plate splined to a clutch hub at a first spline connection portion having a plurality of spline teeth arranged on an inner periphery of the first clutch plate, wherein the first clutch plate comprises: - a friction facing having a plurality of grooves (76, 76') each extending radially along the friction facing and - a plurality of vent holes in the spline teeth proximate the first spline connection portion, each of the plurality of vent holes aligned with a respective groove (76, 76') in a radial direction and allowing an airflow in an axial direction; - a second clutch plate splined to a clutch drum at a second spline connection portion having a plurality of spline teeth arranged on an outer periphery of the second clutch plate, each of the plurality of spline teeth having a recess at a central position of the spline projection portions in an outwardly radial edge configured to form an open space when the second clutch plate is engaged with spline teeth of the clutch drum, thereby defining a vent opening for allowing an airflow in an axial direction at the spline connection portion with the clutch drum; wherein the friction facing is configured to press a friction surface against the second clutch plate when connecting the clutch; and - a cover member including an outside air intake hole to receive outside air into the sealed space and an outside air discharge hole to exhaust airflow from the sealed space to the outside. - a first clutch plate splined to a clutch hub at a first spline connection portion having a plurality of spline teeth arranged on an inner periphery of the first clutch plate, wherein the first clutch plate comprises: - a friction facing having a plurality of grooves (76, 76') each extending radially along the friction facing and - a plurality of vent holes in the spline teeth proximate the first spline connection portion, each of the plurality of vent holes aligned with a respective groove (76, 76') in a radial direction and allowing an airflow in an axial direction; - a friction facing having a plurality of grooves (76, 76') each extending radially along the friction facing and - a plurality of vent holes in the spline teeth proximate the first spline connection portion, each of the plurality of vent holes aligned with a respective groove (76, 76') in a radial direction and allowing an airflow in an axial direction; - a second clutch plate splined to a clutch drum at a second spline connection portion having a plurality of spline teeth arranged on an outer periphery of the second clutch plate, each of the plurality of spline teeth having a recess at a central position of the spline projection portions in an outwardly radial edge configured to form an open space when the second clutch plate is engaged with spline teeth of the clutch drum, thereby defining a vent opening for allowing an airflow in an axial direction at the spline connection portion with the clutch drum; wherein the friction facing is configured to press a friction surface against the second clutch plate when connecting the clutch; and - a cover member including an outside air intake hole to receive outside air into the sealed space and an outside air discharge hole to exhaust airflow from the sealed space to the outside.