PURPOSE: To provide a joint avoiding overload while maintaining sealed properties between a manifold and a throttle body by arranging retaining means retaining a lug in a slot forming an unstressed joint between the throttle body and the manifold.

CONSTITUTION: A synthetic resin intake manifold 18 and a throttle body 30 are jointed together by sliding a cylindrical sleeve 34 extending from the throttle body 30 into an opening 19 in the manifold, thereby a joint can be formed. At this time, two lugs 32 arranged on the throttle body 30 are engaged with lug receiving slots 20 arranged on the manifold 18 so as to provide positive angular and linear alignment, and a clearance between the throttle body 30 and the manifold 18 is sealed by two O-rings 38 intervening between the throttle body 30 and the manifold 18. A U-shaped pin fits through holes in the slots 20 to hold the lugs 32 therein and snaps into a retainer clip 22.