To reduce the amt. of hydrocarbon accompanied to a regeneration region by used particles in a fluidizing method bringing a hydrocarbon raw material into contact with fluidized particles to generate used particles on which a carbonaceous deposit is accumulated and circulating the used particles to the regeneration region to regenerate the same.

Used particles are sent to a cyclone separator 26 from a reactor 15 through an elongated dilution phase stripper 30 while fluidized by a stripping medium such as water or steam and separated from the stripping medium to be transferred to a regenerator 8.