A dust-exhaust acceleration face of a dust-exhaust assistant member is disposed so as to face a top face of a heat radiating member of a production facility or the like so that a gap between the top face of the heat radiating member and the dust-exhaust acceleration face of the dust-exhaust assistant member is occupied by ascending air flows, each having a falling velocity (terminal velocity) that is not accelerated beyond a fixed velocity, to form a balanced state between the size of an object, such as a dust particulate or a chemical substance particulate, and air resistance when the object is freely falling in the air; thus, the object, such as a dust particulate and a chemical substance particulate, is prevented from falling onto the heat radiating member.