A motor-driven airflow control device for controlling a throttle valve fixed to a throttle valve shaft by a motor by transmitting the rotation of the motor to the throttle valve shaft through a reduction gear, said motor-dirven airflow control device comprising: a rotation angle sensor for detecting the rotational position of the throttle valve shaft at the end on the side of the reduction gear of the throttle valve shaft, wherein the rotation angle sensor comprises: a substrate; a rotated detection element; a gear cover; a resin cover; energizing conductors (3A; 3a) for being annularly arranged on said substrate, and generating magnetic fields by applying a current; an exciting conductor for being fixed to said rotated detection element and spaced from and not in contact with said energizing conductors (3A; 3a) to generate a current according to the rotational position of the rotated detection element through electromagnetic induction; and receiving conductors (3B; 3b) for being arranged on the substrate to generate currents according to the current flowing in said exciting conductor; wherein the substrate is attached to the gear cover, whereby said gear cover is made of a resin material and is adapted to cover the reduction gear and wherein the resin cover covers a substrate mounting space; characterized in that the motor-driven airflow control device further comprises a shield member made of a resin material and which is provided between said exciting conductor provided on the rotated detection element and said energizing (3A; 3a) and receiving conductors (3B; 3b) provided on the substrate to cover said energizing (3A; 3a) and receiving conductors (3B; 3b) to shield said energizing (3A; 3a) and receiving conductors (3B; 3b) from ambient air; and in that the motor-driven airflow control device further comprises a positioning pin which is provided on the gear cover. a substrate; a rotated detection element; a gear cover; a resin cover; energizing conductors (3A; 3a) for being annularly arranged on said substrate, and generating magnetic fields by applying a current; an exciting conductor for being fixed to said rotated detection element and spaced from and not in contact with said energizing conductors (3A; 3a) to generate a current according to the rotational position of the rotated detection element through electromagnetic induction; and receiving conductors (3B; 3b) for being arranged on the substrate to generate currents according to the current flowing in said exciting conductor; wherein the substrate is attached to the gear cover, whereby said gear cover is made of a resin material and is adapted to cover the reduction gear and an exciting conductor for being fixed to said rotated detection element and spaced from and not in contact with said energizing conductors (3A; 3a) to generate a current according to the rotational position of the rotated detection element through electromagnetic induction; and receiving conductors (3B; 3b) for being arranged on the substrate to generate currents according to the current flowing in said exciting conductor; wherein the substrate is attached to the gear cover, whereby said gear cover is made of a resin material and is adapted to cover the reduction gear and wherein the resin cover covers a substrate mounting space; characterized in that the motor-driven airflow control device further comprises a shield member made of a resin material and which is provided between said exciting conductor provided on the rotated detection element and said energizing (3A; 3a) and receiving conductors (3B; 3b) provided on the substrate to cover said energizing (3A; 3a) and receiving conductors (3B; 3b) to shield said energizing (3A; 3a) and receiving conductors (3B; 3b) from ambient air; and in that the motor-driven airflow control device further comprises a positioning pin which is provided on the gear cover.