PURPOSE: To enable a throttle valve to be depressed positively toward its entering position even if an excessive sliding resistance is found between the throttle valve and a guiding cylinder by a method wherein a floating of wire in its returning direction is regulated in a carburetor in which a piston type throttle valve is forwarded or retracted by a wire.

CONSTITUTION: A floating movment restricting member 26 acting as means for fixing the end of a wire for restricting a floating movement of the wire 12 in its returning direction regulates a body 17 to disengage from the engagement part 22 by engaging the locking claw 29 in the slit 23, and in turn resiliently depressing an annular member 18 upwardly under a resilience of the horizontal part 31. As a result, the wire 12 is regulated to move upward freely by an engagement between the body 17 and the engaging part 22, further its free and downward movement is regulated by an abutment of the annular member 18 against the upper surface of the horozontal part 31. That is, when the wire 12 is to be returned, the wire 12 depresses the throttle valve 5 downward through the annular member 18 and the horizontal part 31. Thereby, the throttle valve 5 is positively returned downward.