To protect a stirring blade from damage and deformation by detecting biting of a solid foreign matter by the stirring blade in a fluidization treatment tank at an early stage.

Pressure of the inflow side at the time of rotation of a hydraulic motor 29 is detected by a pressure sensor 55 at the time when a solid foreign matter such as a rock, etc., bites in between a stirring plate main body of a stirring blade provided in the inside of a fluidization-treatment tank and a bottom surface of the fluidization treatment tank. Thereafter, biting of the solid foreign matter by this stirring blade is released by magnetizing an electromagnetic pilot part 54P of an electromagnetic change-over valve 54 for a specified period of time from a timer circuit 56 and reversing the stirring blade at the time of exceeding set pressure of this pressure sensor 55.