A device for supplying fuel to an engine, the fuel supply device comprising: a fuel tank; a fuel supply route for supplying to the engine fuel that has been collected in the tank; a filter provided to the fuel supply route; a first fuel pump provided downstream of the filter in a fuel supply direction on the fuel supply route; a merge and discharge unit for merging and discharging fuel, the merge and discharge unit being provided to a site between the fuel tank and the filter on the fuel supply route; a first fuel return route for returning the fuel of the engine to the merge and discharge unit; and a second fuel return route for returning to the fuel tank the fuel discharged from the merge and discharge unit; wherein: the merge and discharge unit has: a reservoir unit in which fuel can be collected; a first merge unit for merging into the reservoir unit the fuel from a site upstream of the merge and discharge unit on the fuel supply route; a second merge unit for merging into the reservoir unit the fuel from the first fuel return route; a first discharge unit for discharging a portion of the fuel in the reservoir unit to a site downstream of the merge and discharge unit on the fuel supply route; and a second discharge unit for discharging a remaining portion of the fuel in the reservoir unit into the second fuel return route, and wherein the first discharge unit of the merge and discharge unit is arranged in sites below the reservoir unit, the second discharge unit is arranged at a site above the reservoir unit, characterized in that the first merge unit and the second merge unit of the merge and discharge unit are arranged in sites below the reservoir unit. a fuel tank; a fuel supply route for supplying to the engine fuel that has been collected in the tank; a filter provided to the fuel supply route; a first fuel pump provided downstream of the filter in a fuel supply direction on the fuel supply route; a merge and discharge unit for merging and discharging fuel, the merge and discharge unit being provided to a site between the fuel tank and the filter on the fuel supply route; a first fuel return route for returning the fuel of the engine to the merge and discharge unit; and a second fuel return route for returning to the fuel tank the fuel discharged from the merge and discharge unit; wherein: the merge and discharge unit has: a reservoir unit in which fuel can be collected; a first merge unit for merging into the reservoir unit the fuel from a site upstream of the merge and discharge unit on the fuel supply route; a second merge unit for merging into the reservoir unit the fuel from the first fuel return route; a first discharge unit for discharging a portion of the fuel in the reservoir unit to a site downstream of the merge and discharge unit on the fuel supply route; and a second discharge unit for discharging a remaining portion of the fuel in the reservoir unit into the second fuel return route, and wherein the first discharge unit of the merge and discharge unit is arranged in sites below the reservoir unit, the second discharge unit is arranged at a site above the reservoir unit, characterized in that the first merge unit and the second merge unit of the merge and discharge unit are arranged in sites below the reservoir unit. the merge and discharge unit has: a reservoir unit in which fuel can be collected; a first merge unit for merging into the reservoir unit the fuel from a site upstream of the merge and discharge unit on the fuel supply route; a second merge unit for merging into the reservoir unit the fuel from the first fuel return route; a first discharge unit for discharging a portion of the fuel in the reservoir unit to a site downstream of the merge and discharge unit on the fuel supply route; and a second discharge unit for discharging a remaining portion of the fuel in the reservoir unit into the second fuel return route, and wherein the first discharge unit of the merge and discharge unit is arranged in sites below the reservoir unit, the second discharge unit is arranged at a site above the reservoir unit, characterized in that the first merge unit and the second merge unit of the merge and discharge unit are arranged in sites below the reservoir unit. a reservoir unit in which fuel can be collected; a first merge unit for merging into the reservoir unit the fuel from a site upstream of the merge and discharge unit on the fuel supply route; a second merge unit for merging into the reservoir unit the fuel from the first fuel return route; a first discharge unit for discharging a portion of the fuel in the reservoir unit to a site downstream of the merge and discharge unit on the fuel supply route; and a second discharge unit for discharging a remaining portion of the fuel in the reservoir unit into the second fuel return route, and wherein the first discharge unit of the merge and discharge unit is arranged in sites below the reservoir unit, the second discharge unit is arranged at a site above the reservoir unit, characterized in that the first merge unit and the second merge unit of the merge and discharge unit are arranged in sites below the reservoir unit.