A fuel supply device configured to supply fuel from an inside of a fuel tank to an internal combustion engine includes: a cover body that is installed to an upper wall of the fuel tank; a pump unit that is placed on a bottom wall of the fuel tank and is configured to discharge the fuel from the inside of the fuel tank toward the internal combustion engine; and a coupling stay that couples between the cover body and the pump unit. The coupling stay includes: an upper stay that extends on a lower side of the cover body; and a lower stay that is installed to the pump unit and is slidably fitted to the upper stay in a top-to-bottom direction. A stress concentrating portion, which reduces a section modulus to concentrate a stress around the stress concentrating portion, is formed at a specific location of the lower stay.