PURPOSE: To collect only a substance to be sampled even if impurities are floated on the surface of the substance to be sampled like a layer by descending a sampling pipe while blowing out gas from the lower end, and absorving the substance to be sampled under reduced pressure.

CONSTITUTION: A travelling track 11 and a manipulator 12 are operated so that the leading end part of an arm 13 is positioned on the upper part of molten iron 18 through a sampling port 28 of a tub 17, and an opening/closing valve 20 is closed to close a discharge pipe 21 and actuate an air compressor. When the arm 13 is descended, the sampling tube 19 blows away slag 29 floating on the surface of the molten iron 18 and reaches into the molten iron 18. When the opening/closing valve 20 is opened and the compressed air is discharged from the discharge pipe 21, the inside of the sampling tube 19 is made negative pressure and the molten iron 18 is made flow into the sampling tube 19. While keeping said state, the arm 13 is ascended.