PURPOSE: To determine the descending speeds, layer thicknesses and angles of inclination of charging materials and to effectively detect the behaviors thereof by inserting two pieces of upper and lower hollow pipes mounted with magnetism detecting elements in their leading ends into the charging material layers in the furnace only during measuring and processing the magnetism output signals in prescribed positions.

CONSTITUTION: Hollow pipes 3 of which the leading ends are made of nonmagnetic materials are inserted into the prescribed positions in a blast furnace 1 through the measuring holes provided in the wall of said furnace, and the magnetism of the charging materials is detected by the magnetism detecting elements 2 mounted in the leading ends of the pipes 3. The detected outputs are signal processed through an amplifier 7 and a signal processor 8, and are recorded 9. Based on the results of the record, layer thicknesses are determined from the descending speeds of the charging materials. The descending speed distribution and layer thickness distribution in a radial direction are measured by performing detection while moving the pipes 3 radially. As a result, the descending speeds, layer thicknesses, angles of inclination, etc. in the arbitrary positions in the furnace are detected in an extremely natural state.