Blast apparatus provided with blast chamber having suppressed adhesion of spray material and dust on inner wall surface

To provide a blast chamber having suppressed adhesion of a spray material and dust on the inner wall of the blast chamber in a blast apparatus for performing blasting by spraying a spray material from a blast nozzle to a subject to be processed. Provided is a blast chamber, which has one or more external air suction ports provided in the ceiling surface or the side wall surfaces thereof, said external air suction ports sucking external air into the blast chamber and making the sucked air flow along the inner wall surface of the blast apparatus. Consequently, adhesion of the spray material and dust is eliminated due to the flow of the external air sucked into the blast chamber.