To provide a remaining thickness detecting method of refractories, used to the operating part of an industrial furnace, which is capable of detecting the impossibility of detection due to the blocking of fluid passage previously and effecting trouble preventing measure quickly thereafter, upon detecting the remaining thickness of the refractories by the changes of the flow rate of fluid, a pressure and the like through the fluid passage in the refractories.

The remaining thickness of refractories used for the operating part of an industrial furnace is detected by a method wherein a fluid passage 2 is provided from the back surface side of refractories to the position of a predetermined thickness toward the operating surface side in the refractories to measure the change of flow rate or pressure of the fluid, supplied into or discharged out of the fluid passage 2, by flow rate detectors 6a, 6b or pressure detectors, arranged at the supplying side and discharging side of fluid connected to the fluid passage 2. In this case, the remaining thickness of refractories 1 is detected by the change and the detection of non-passing of the fluid in the fluid passage is also detected.