PURPOSE: To enable the continuous measurement of inclusion in high temp. molten metal with an insulating tube improved in heat resistance by arranging an orifice in the insulating tube constituting a probe body to allow the molten metal to flow in and out and fitting an inner electrotrode and an outer cylinder in the insulating tube.

CONSTITUTION: An inner and outer electrodes 31, 32 in the inner and outer cylinders are insulated by an insulating refractory material-made quartz tube 30 constituting the probe body. The upper end of the quartz tube 30 is supported by a probe head 35 through a gasket 34 and the inner and outer electrodes 31, 32 are connected with electrode bars 36, 37. A cover part of the inner cylinder constituting the inner electrode 31 constitutes a heat shut-off shield part 40. At the time of measuring, the inner part of the quartz tube 30 is evacuated and the molten metal is sucked into the qualtz tube 30 through the orifice 33 arranged at the lower part. At this time, the variation of electric resistant value is detected to quantify the inclusion.