PURPOSE: To prevent a powdery material from being mixed with the gas contg. dust and from entering into a dust collecting device and to improve the separation and collecting efficiency by connecting the gas inlet opening of the dust collecting device with the top cover part of the hopper of a hopper dryer, etc., through a gas discharge pipe so as to communicate with the hopper.

CONSTITUTION: A cylindrical punching body 16 having a number of fine openings 11 and a cylindrical filter cloth body 20 received in the punching body 16 constitute the dust collecting device 1. The gas inlet opening 4 of this dust collecting device 1 is connected with the top cover part 61 of the hopper 51 of a hopper dryer 50, etc., through the gas discharge pipe 2 so as to communicate with the hopper, and the dust collecting device 1 is connected with a collected dust receiving part 7. As a result, the powdery material is prevented from being mixed with the gas contg. dust and from entering into the dust collecting device, so that the separation and collection efficiency is improved and the gas is recovered without remaining in the hopper. Moreover, the catching efficiency of the gas contg. dust is improved, and the scattering of powder and dust in the surroundings is prevented.