To quickly melt unmolten material by introducing the unmolten material into a tune in the state that the part or all of high temperature molten metal is introduced into the tube, and positively bringing the molten metal into contact with the unmolten material while oscillating it.

Unmolten material 5 is introduction into a tube 1 in the state that all or part of molten metal 6 exists, the tube 1 is oscillated in a swing shaft 2, and the metal 6 is externally heated while positively bringing the metal 6 into contact with the material 5. Thus, the material 5 and the metal 6 are agitated, and the material 5 is rapidly dipped in the metal 5 to suppress the oxidation of the surface, and it is externally heated while fully bringing into contact with it to heat exchange, and hence it can very effectively and quickly melted.