A melting furnace includes a gas supplying unit configured to protrude inwardly of the melting furnace to supply a gas to the melting furnace, the gas supplying unit including a gas supplying pipe configured to penetrate the melting furnace to protrude inwardly of the melting furnace and configured to have a nozzle hole formed at a front end thereof; and a cooling passage pipe provided outside the gas supplying pipe to include a second cooling passage through which a cooling liquid flows, the second cooling passage being directly connected to a first cooling passage through which the cooling liquid is circulated along a wall of the melting furnace.