PURPOSE: To contrive smooth operation of an engine while reducing the friction between a guide cylinder and a throttle valve by controlling the air flow rate passing through the piston type throttle valve while allowing said valve to slide in the guide cylinder and go back and forth from and into a suction air passage.

CONSTITUTION: A cylindrical anti-frictional wear member 12 is forcedly inserted into and fixed on the inner surface of the guide cylinder 2c of a piston type throttle valve 4. The anti-frictional member 12 is obtained by sintering cupper alloy fine powder to form an aggregate 12b of metal particles on the inner surface of mild steel made cylindrical lining 12a, and coating the relatively rough surface of said inner surface with ethylene tetrafluoride 12c. The piston type throttle valve 4 is smoothly elevated with use of the anti-frictional wear member 12.