An adjustable air diffuser is disposed in an airflow channel into which travelling wind is directed through an opening provided in a bumper face. The diffuser substantially opens and closes the airflow channel by using a movable louver blade driven by an actuator. An upper part of the diffuser is disposed to face a rear wall of the bumper face and is attached to a bumper beam extending substantially along a vehicle width direction. A lower part of the diffuser is either one of attached to a vehicle body structural member and a load transmission member projecting forward from the vehicle body structural member. The upper part of the diffuser and the bumper beam are connected with each other with an upper bracket having a weak portion that is configured to be broken in response to pivotal movement of the diffuser relative to the bumper beam.