PURPOSE: To accurately grasp the layer thickness and the grain size of charged material in a blast furnace.

CONSTITUTION: A sampling device in combination of heat resistant sampling bags 3 and a supporting frame 1 is inserted from manholes 8, 9 for changing a movable armor through wire ropes 4, 5, 6, 7 fitted to both ends in the longitudinal direction of the supporting frame 1. The sampling device is arranged on the surface 11 of the raw material in the radial direction in the blast furnace 2 in suspension of blasting, and thereafter, the raw material 12 is charged and sampling device is pulled up through the wire ropes 4, 5, 6, 7, and the raw materials 12 piled on the sampling bags 3 are sampled to measure the layer thickness and the grain size of the charged material in the radial direction in the blast furnace. By this method, gas flow distribution in the furnace is suitably kept and the stable operation can be executed.