To solve a problem of stopping conveying work due to clogging of a suction port with earth and sand and stopping of a screw by a large stone caused by early suction of only moisture at start of suction.

Separation of the moisture from the earth and sand is prevented by stirring by stirring machine, the large stone is sorted by a mesh stick, the earth and sand become liable to be sucked by making the body form of the suction clogging prevention device into a dome shape by utilizing an action that a sucked object adheres around the device when sucking the earth and sand, thereby increasing working efficiency and increasing interests without stopping sucking work.