To make a carburetor provided with a manual operation type altitude compensation mechanism capable of easily returning to shipping standard conditions while making it easy to materialize optimal air fuel ratio according to altitude at which the carburetor is used.

In the carburetor with the highland compensation mechanism provided with the highland compensation mechanism materializing appropriate air fuel ratio according to the altitude at which the carburetor is used, the altitude compensation mechanism is provided with a manual operation type air flow rate adjusting valve 5 provided in an air bleed passage 3 and with a bypass passage 51 bypassing the air flow rate adjusting valve 5, materializes air flow rate appropriate to a flatland by only the bypass passage 51 under a condition where the air flow rate adjusting valve 5 is closed at a standard position for the flatland of the air flow rate adjusting valve 5, and executes altitude compensation by increasing air flow rate in the air bleed passage 3 by manually opening the air flow rate adjusting valve 5 as altitude is getting higher.