PROBLEM TO BE SOLVED: To provide a plastic greenhouse which can be more inexpensively constructed while having sufficient strength against torsion and the like.SOLUTION: The frame structure of a plastic greenhouse is made up as follows: a roof surface part and side surface parts are structured by joining, at intervals, a plurality of longitudinal frames formed by connecting inside longitudinal pipes and outside longitudinal pipes via connecting metal fittings, to horizontal pipes set up in a ridge direction. In the structure, the top end parts of a pair of the right and left longitudinal frames at one side are connected via joint materials at the center of the roof surface part； and the joint materials are each formed into an almost angle shape, and structured so that a primary connection body connecting the respective inside longitudinal pipes of a pair of the right and left longitudinal frames at one side are connected to a secondary connection body connecting the respective outside longitudinal pipes with one another, via connection materials each having a prescribed length.
