A particulate material collecting apparatus including a cylindrical member defining therein a spiral flow chamber for forming a spiral flow of gas therein, an inlet duct and an outlet duct connected to the cylindrical member tangentially to the inner circumferential surface thereof, and a hollow inverted pyramidical member secured to the lower portion of the cylindrical member. A spiral flow guide plate having a convex surface curved radially outwardly of the cylindrical member is interposed between the cylindrical member and the inverted pyramidical member. The spiral flow guide plate is positioned so as to define two openings, one opening being located on the upstream side of the spiral flow of gas and the other opening being located on the downstream side of the spiral flow of gas. The spiral flow of gas is introduced from the spiral flow chamber through the upstream side opening into a material collecting space defined between an inner wall portion of the inverted pyramidical member and a collected material guide plate secured to the spiral flow guide plate to extend parallel to the inner wall portion, so that particulate material incorporated in the spiral flow of gas is separated by inertia from the gas and collected in the inverted pyramidical member.