To provide a low-cost combustion device and metal melting furnace, which prevent generation of black smoke or harmful gas even if burning waste plastic fuel, and is used for a burner of a boiler, a metal melting furnace or the like for efficiently melting metal such as an aluminum can.

This combustion device comprises: a tubular combustion cylinder having an exhaust port in an erected upper part; an air supply pipe of a multistage installed in a center part of the combustion cylinder such that the air supply pipe is erected, and formed with a large number of air supply holes capable of supplying air into the combustion cylinder; an air supply device using a blower supplying air to the air supply pipe; a fuel storage tray provided inside the combustion cylinder of a lower peripheral part of the air supply pipe, storing the waste plastic fuel; a water tank having a plurality of pipes jetting water vapor to combustion flame, provided in a lower position inside the combustion cylinder; a water supply device supplying water to the water tank: and an opening/closing door installed to the combustion cylinder such that the fuel can be supplied into the fuel storage tray.