To provide a circulation fluidized bed boiler device and its operation control method for solving problems on the aggregation of particles generated in a circulation fluidized bed system and problems on the corrosion and dirt disturbance of a heat transfer surface of a convection heat transfer part, at the same time.

The operation control method is provided for the circulation fluidized bed boiler device which has a furnace 1 for combustion of coal, various wastes or biomass, a cyclone 3, the convection heat transfer part 6, and a circulation line 44. Therein, trapped particles trapped by the cyclone 3 and gas involved in the particles flow down to a particle trapping box 4 at a speed of 1-3 m/sec. Thus, fluidized air is supplied from the lower part of the particle trapping box to give an upward gas flow speed thereto. The upward speed of the fluidized air is adjusted to a speed sufficiently higher than an average downward fall-down speed of the trapped particles to secure a sufficient time for the fluidized air to reside in or pass through the fluidized bed to separate and classify the particles.