To realize desired collection and disposal of dust by a simple work by providing a storing drum rotating with an axial center line to be front and rear directions of a chassis as a center and providing a spiral blade for feeding or discharging dust to be a collected object according to a rotating direction of the storing drum.

A storing drum 1 is set to selectively rotate in a forward direction to be the so-called storing direction or a backward direction to be the so-called discharging direction. The storing drum 1 is provided with a spiral blade 2 feeding or discharging tree chips to be dust according to a rotating direction of the storing drum 1, providing a base end successively with an inner wall and directing an upper end to an axial center line side of the storing drum 1. The spiral blades 2 are made the so-called pair and is set to embody effective feeding or discharging of tree chips. The spiral blade 2 is set so that the height may be almost 1/4 to 1/2 of a radius R of the storing drum 1.