Abstract: In a ball plug valve (10 ) which has a main opening (14 ) and an auxiliary opening (14 ) A serving as the inlet openings of a flow through hole (13 ) of a ball (12 ) and which has a sectorial opening (15 ) serving as an outlet opening thereof; it is set so that a tip (15 ) A of the sectorial opening (15 ) is in a first sealing region (17 ) A provided by an outlet sealing member near an outlet passage when the valve is fully closed, while the tip (15 ) A of the sectorial opening (15 ) passes across the outlet passage and enters a second sealing region (17 ) B provided by an outlet sealing member when the valve is fully opened.