To provide a cyclone which can improve collecting efficiency by preventing re-scattering of separated particles.

Slits 13 are formed in a conical cylinder 12 and an outside chamber 14 is provided by surrounding the outsides of the slits 13 to make only particles D enter the outside chamber 14 via the slit 13. By forming the slits 13 in the conical cylinder 12 and surrounding the outside thereof by the outside chamber 14, only the particles D can be recovered into the outside chamber 14 via the slit 13 without generating flow of a gas G to the outside chamber 14 and thereby re-scattering of the separated particles D is prevented to improve collecting efficiency.