To obtain an efficient and optimum cleaning period by monitoring the adhesion of powder adhering to the inner passage of a dispersion ring when evaporated steam passes by the same.

This centrifugal drying machine has a main spindle 21 which is freely rotatably arranged in a heat transfer cylinder 5, blades 43 which rotate together with the main spindle 21 and rotate the inside surface of the heat transfer cylinder and the dispersion ring 17 which disperses raw sludge supplied in the upper side of the heat transfer cylinder 5 along the inner wall surface of the heat transfer cylinder 5. The raw sludge is given the heat by the heat transfer cylinder 5, by which the moisture in the raw sludge is evaporated and the evaporated steam is discharged outside from a steam discharge port 11 through the dispersion ring 17. The pressure difference between the upper side and lower side of the dispersion drying 17 is measured by a pressure sensor 27 and the adhesion of the powder of the dispersion ring 17 is monitored in accordance with the pressure difference.