To provide a method of effectively depositing metal and other inorganic matter dissolved in magma.

Water 30 is injected into magma 22 of a volcano 17 to generate high pressure water in which the magma 22 is dissolved within a cover 18 surrounding the magma 22 and deposit inorganic material dissolved in the high pressure water corresponding to the dissolution temperature. When the water 30 is injected into the magma 22, steam is generated from the surface of the magma 22. At this time, the higher the pressure of the water is, the more various kinds of the inorganic material dissolved in the magma 22 are dissolved in the high pressure water to turn it into steam and extracted from a stream takeoff port to deposit the target inorganic matter. And a high pressure steam extracting pipe may be inserted into the magma 22 of the volcano 17 to directly take out high pressure steam contained in the magma 22 and deposit inorganic material dissolved in this high pressure water corresponding to the dissolution temperature.