PURPOSE: To improve assemblability in a relay shaft in a condition mounted in a vehicle, by forming an automatic drive lever and its related parts into a component, in an intake air throttle valve opening/closing device for an internal combustion engine provided with the automatic drive lever connected to an automatic drive mechanism.

CONSTITUTION: An automatic drive lever subassembly 31, movable side spring guide 35, spring 33 and a fixed side spring guide 34 are successively built in a collar subassembly 32, also to hook respectively one end of the spring to the fixed side spring guide 34 and the other end to the automatic drive lever subassembly 31, so as to constitute an automatic drive lever component 36. In this constitution, at assembly time in a relay shaft 2 of an intake valve cylinder 1, the fixed side spring guide 34 is fitted not rotatably to a two-face width of the relay shaft 2 through an oval-shaped hole, according to this fitting, to fix one end of the spring 33.