To provide a furnace wall deposit detection method and apparatus for easily and accurately detecting a deposit deposited to a furnace wall.

A furnace wall deposit detection method for detecting a deposit 11 deposited to the furnace wall of a furnace composed of bricks 10 having no conductivity measures the strength of electromagnetic waves radiated from the bricks 10 and the deposit 11, detects the deposit 11 on the basis of the measured strength of the electromagnetic waves, and specifies the position of the deposit 11 from recognition of a reception direction in detecting the deposit 11.