There is provided a greenhouse windbreak mechanism which is less prone to collapse of cultivation greenhouses, even when the greenhouse windbreak mechanism is constructed along with the cultivation greenhouses such as plastic greenhouses with relatively-lower strength and is subjected to storm winds or strong monsoons. There are provided a windbreak fence which surrounds one or more cultivation greenhouses and is annularly placed to be erected with a larger height than that of the cultivation greenhouses, a ventilation portion which is formed, at an upper portion of the windbreak fence, to have a predetermined longitudinal width from the upper end of the windbreak fence and includes a plurality of through holes which are dispersedly placed and a plurality of baffle plates which form a plurality of through holes in its entire surface or partially for passing strong winds therethrough when they are laterally placed above the cultivation greenhouses. The ventilation portion and the baffle plates alleviate strong winds intruding into the inside of the mechanism by getting around the upper end of the windbreak fence, when the strong winds impinge on the windbreak fence.
