A fuel supply device for carburetors in which a first level sensor (10) for maintaining a reference fuel liquid level in a fuel chamber (7) is provided separate from the fuel chamber; a second level sensor (20) used to maintain properly a fuel flow rate in a slow operation zone (6) and a third level sensor (16) used to maintain properly a fuel flow rate in a main operation zone (1) are arranged close by the first level sensor; and a mixture with a proper air-fuel ratio can always be supplied to an engine even if the fuel liquid level in the fuel chamber fluctuates and the entire carburetor inclines, without being affected thereby.