Provided is a dust flocculating duct which has a simple configuration and is capable of reducing the number of particulates by increasing the number of times when the particulates in dust collide with one another and by facilitating flocculation and of increasing an apparent diameter of each of the particulates. The dust flocculating duct comprises: an extension pipe (502), a suction hose (504), and a joining section (505) as, a frictional electrification passage part (161) disposed in the extension pipe and friction-electrifying the pieces of dust, and a collision promotion passage part (162) disposed in the joining section, causing the pieces of dust electrified by the frictional electrification passage part to collide with each other, and facilitating formation of dust masses (clusters). The frictional electrification passage part includes a first frictional electrification part made of a first material and a second frictional electrification part made of a second material. The collision promotion passage part is made of a third material. A contact potential difference of the first material is larger than a contact potential difference of the third material and the contact potential difference of the third material is larger than a contact potential difference of the second material.