A fuel delivery device for a fuel tank comprising a float chamber for sucking fuel in a normal state, a sub chamber for sucking a small quantity of fuel remaining within a tank and a communication chamber for communicating the float chamber and the sub chamber to each other in lower portions thereof En the fuel delivery device for a fuel tank, a sub float chamber is provided above the sub chamber, the sub float chamber has a gas discharge port communicating with-the fuel tank in an upper portion, a vent hole communicating with the sub chamber in a lower portion and a sub float valve within, and the sub float valve ascends and descends in accordance with a quantity of an excess fuel returned to the sub float chamber from the engine so as to open and close the vent hole. Further, in the fuel delivery device for a fuel tank, a bypass passage having bent passage sections of down, up and down which is formed by arranging a lower separation wall having a gap in an upper portion with respect to a communication passage for feeding out fuel from the sub chamber to the communication chamber and an upper separation wall having a gap in a lower portion with respect to the communication passage in order is formed within the sub chamber and the bypass passage and the communication passage are connected to each other.