To provide a film type carburetor wherein intake negative pressure in a further upstream than the throttle valve of an intake air passage is relieved to the air vent chamber of a constant pressure fuel supply mechanism.

A constant pressure fuel chamber 19 is partitioned from the air vent chamber 30 on the lower wall of a carburetor body 12 so as to hold a film 18 there between. Air passages 17, 22 extending to the air vent chamber 30 from the further upstream part than the throttle valve 13 of the intake air passage 31 is provided, and the intake negative pressure which gets suddenly strong right after the engine speed is reduced is introduced to the air vent chamber 30.