Abstract: The inventive Quonset-type pipe-frame greenhouse is constructed with: a plurality of main rib members each in a semicircular or inverted U-shaped form erected on the ground in parallel with each other and connected together with at least one longitudinal connecting member to form a main room; a plurality of auxiliary rib members each straddling on the ridge line of the main room and connected together with at least one auxiliary longitudinal connecting member to form a monitor roof-like protrusion; and transparent sheet members of a plastic resin for the walls of the main room and the monitor roof-like protrusion each capable of being turned up at the lower end to make an opening for ventilation according to need. The inventive greenhouse is advantageous in the improved ventilation in the upper part of the room to assist healthy growth of the plants and in the improved aerodynamic strength of the structure capable of resisting a strong wind without the danger of falling down.