A fuel supply device has a module installed in a fuel tank. The module has a cap and a support pillar arranged between the cap and a bottom of the fuel tank. The support pillar supports a suction filter and a level sensor to use the bottom of the fuel tank as a base point for defining proper positions. The cap supports a valve relevant to ventilation of the fuel tank. The valve is supported by a base portion. The valve is positioned in the support pillar. The valve and the support pillar are arranged to overlap each other along the height direction. Various components are arranged in the small cap.