Two nozzles 37 in pair are provided along an inner circumferential surface 21a of a concavity 21, air is blown out in a space from a blowout hole 37a provided at a tip end portion of the nozzle from a side where the nozzle 37 is provided aiming at an opposite side along an inner circumferential surface of the space and a powder contained in the concavity 21 is caused to rise up in the space, whereby the condition of the powder mixed with the air within the space is improved.