A sealing device sealing so as to prevent a sealed fluid in a machine inner side from leaking to a machine outer side between a housing and a rotating shaft which is inserted to a shaft hole provided in said housing, the sealing device comprising: a seal flange which is installed to an outer periphery of said rotating shaft; a seal lip (24, 27, 28) which is installed to an inner periphery of the shaft hole of said housing; and the seal lip (24, 27, 28) slidably coming into contact with the seal flange over an entire periphery, wherein the sealing device comprises: a thread groove (15, 35) which exerts a fluid pumping action when said rotating shaft rotates, and wherein said thread groove (15, 35) is provided at a position which does not intersect a contact area where said seal lip slidably comes into contact with said seal flange over the entire periphery, characterised in that a thread groove forming area is provided in a machine outer side end face of said seal flange by setting said thread groove (15, 35) in a part of the machine outer side end face of said seal flange, and a thread groove non-forming area which is not provided with said thread groove (15, 35) is provided in an outer peripheral side of said thread groove forming area, wherein said seal lip (24, 27, 28) is slidably brought into contact with said thread groove non-forming area, and wherein an annular projection is provided in an inner peripheral side of said seal lip (24, 27, 28) toward said seal flange, and a micro gap is provided between said projection and said seal flange. a seal flange which is installed to an outer periphery of said rotating shaft; a seal lip (24, 27, 28) which is installed to an inner periphery of the shaft hole of said housing; and the seal lip (24, 27, 28) slidably coming into contact with the seal flange over an entire periphery, wherein the sealing device comprises: a thread groove (15, 35) which exerts a fluid pumping action when said rotating shaft rotates, and wherein said thread groove (15, 35) is provided at a position which does not intersect a contact area where said seal lip slidably comes into contact with said seal flange over the entire periphery, characterised in that a thread groove forming area is provided in a machine outer side end face of said seal flange by setting said thread groove (15, 35) in a part of the machine outer side end face of said seal flange, and a thread groove non-forming area which is not provided with said thread groove (15, 35) is provided in an outer peripheral side of said thread groove forming area, wherein said seal lip (24, 27, 28) is slidably brought into contact with said thread groove non-forming area, and wherein an annular projection is provided in an inner peripheral side of said seal lip (24, 27, 28) toward said seal flange, and a micro gap is provided between said projection and said seal flange. a thread groove (15, 35) which exerts a fluid pumping action when said rotating shaft rotates, and wherein said thread groove (15, 35) is provided at a position which does not intersect a contact area where said seal lip slidably comes into contact with said seal flange over the entire periphery, characterised in that a thread groove forming area is provided in a machine outer side end face of said seal flange by setting said thread groove (15, 35) in a part of the machine outer side end face of said seal flange, and a thread groove non-forming area which is not provided with said thread groove (15, 35) is provided in an outer peripheral side of said thread groove forming area, wherein said seal lip (24, 27, 28) is slidably brought into contact with said thread groove non-forming area, and wherein an annular projection is provided in an inner peripheral side of said seal lip (24, 27, 28) toward said seal flange, and a micro gap is provided between said projection and said seal flange.