To effectively prevent the solidification of granular body by keeping granular body containing a binder in a fluidized state until the working life elapses to invalidate the binding property of the binder.

The granular body (raw material granular body or waste granular body) 2 stored in a raw material hopper (vessel) 1 and containing the binder becomes in the fluidized state in a process of flowing down while being stirred by a stirring structure (fluidizing means) 4 in a mixing chamber 3. When a hardening accelerating material 6 is charged to the granular body 2 in the fluidized state from a charging line 10 connected to the mixing chamber 3 by a blower 5, the binding force of the binder is invalidated to form a dry state granular body 7, which is moved to a retaining chamber 8. After being retained in the retaining chamber 8 for a prescribed time, the dry state granular body 7 is discharged out of the line with a damper opened and simultaneously the excess effective component in the applied hardening accelerating material 6 is sucked in the retaining chamber 8 by the blower 5 from a recovering line 13 connected to the retaining chamber 8 to be recovered and supplied again to the mixing chamber 3 to be reutilized.