A walk-behind self-propelled working machine includes an engine disposed with a crankshaft extending vertically in a downward direction and a cylinder disposed horizontally, and a generator having a drive shaft disposed vertically downward. The drive shaft of the generator and the crankshaft of the engine have respective axes that are disposed on a line perpendicular to an axis of the cylinder, as viewed in plan. The crankshaft and the drive shaft are connected together via a power transmitting mechanism.