A fuel supply device for an engine includes a fuel tank positioned such that, at least when the fuel tank is filled with fuel, a first fuel level in the fuel tank is higher than a minimum required second fuel level in a float chamber. A bypass passage that bypasses a fuel pump is provided, and an on-off valve is disposed in the bypass passage. The fuel supply device is capable of improving a starting characteristic of the engine during an off period of the fuel pump without increasing a head difference between the first and second fuel levels.