PURPOSE: To protect materials when unloaded from the wind blow which comes from the direction where no windbreak is located so as to improve the dustproof performance by allowing a grab bucket to open to the direction where the grab bucket moves in and out.

CONSTITUTION: A grab bucket 3 is allowed to open toward the direction where it (3) moves in and out. In this configuration, when materials are unloaded from the grab bucket 3 with the bucket 3 opened into a hopper 4 of an unloader, the circumference of which is surrounded by a windbreak 6 except a place where the grab bucket 3 moves in and out, the opened grab bucket 3 prevents the wind from coming in through the space where the grab bucket moves in and out. This configuration prevents materials when unloaded from being blown off by the wind permitting no dust to be accumulated.