PURPOSE: To prevent the occurrence of the malfuction of a detector due to vibration by connecting a detecting shaft with a throttle shaft via a flexible coupling, and further making the end part of the detecting shaft a taper shaft part and forming a taper receiving part inside a housing.

CONSTITUTION: A throttle opening detector 10 detects the turning angluar position of a throttle shaft 16 which is connected to a detecting shaft 16. Both the throttle shaft 15 and the detecting shaft 16 are connected by a flexible coupling 26 made of a synthetic resin. The end part of the detecting shaft 16 is made to be a taper shaft part 28, and on the inner surface of a cap part 13 a taper receiving part 29 is formed. The taper shaft part 28 is supported by the taper receiving part 29 through an elastic spring force of an elastic spring member 30. Thus, the occurrence of the malfunction of a detector due to vibration can be securely prevented.