A sealing device comprising a seal ring for sealing a clearance between a rotary shaft and a housing, a rotary shaft, and a housing, said seal ring comprising inclined grooves (15, 115, 215) formed at a sliding surface so as to be arranged in a circumferential direction, and supply grooves (13, 113, 213), wherein a seal portion is formed continuously in the circumferential direction and positioned between the supply grooves (13, 113, 213) and the inclined grooves (15, 115, 215), the seal ring is housed in an annular groove which has a rectangular sectional shape and is formed in an outer periphery of the rotary shaft, said rotary shaft being inserted into a shaft hole of the housing, wherein a side surface (10, 110, 210, 310, 410) of the seal ring includes a sliding surface (S1, S2) which may be slidably brought into close contact with a side wall surface of the annular groove, wherein an outer peripheral surface of the seal ring may be brought into close contact with an inner peripheral surface of the shaft hole, wherein the inclined grooves (15, 115, 215) are formed so as to communicate with an outer-diameter-side end portion of the side surface (10, 110, 210, 310, 410) of the seal ring, characterised in that the supply grooves (13, 113, 213) are communicated with each other through a communication groove which is positioned on the inner diameter side of the seal portion and extends in the circumferential direction, wherein the inclined grooves (15, 115, 215) are formed inclined to the direction of rotation of the rotary shaft from the vicinity of an outer-diameter-side end portion of the communication groove, and wherein the supply grooves (13, 113, 213) are open on a sealed fluid side of the seal ring and extending in a radially outward direction toward inner diameter sides of the inclined grooves (15, 115, 215). a seal ring for sealing a clearance between a rotary shaft and a housing, a rotary shaft, and a housing, said seal ring comprising inclined grooves (15, 115, 215) formed at a sliding surface so as to be arranged in a circumferential direction, and supply grooves (13, 113, 213), wherein a seal portion is formed continuously in the circumferential direction and positioned between the supply grooves (13, 113, 213) and the inclined grooves (15, 115, 215), the seal ring is housed in an annular groove which has a rectangular sectional shape and is formed in an outer periphery of the rotary shaft, said rotary shaft being inserted into a shaft hole of the housing, wherein a side surface (10, 110, 210, 310, 410) of the seal ring includes a sliding surface (S1, S2) which may be slidably brought into close contact with a side wall surface of the annular groove, wherein an outer peripheral surface of the seal ring may be brought into close contact with an inner peripheral surface of the shaft hole, wherein the inclined grooves (15, 115, 215) are formed so as to communicate with an outer-diameter-side end portion of the side surface (10, 110, 210, 310, 410) of the seal ring, characterised in that the supply grooves (13, 113, 213) are communicated with each other through a communication groove which is positioned on the inner diameter side of the seal portion and extends in the circumferential direction, wherein the inclined grooves (15, 115, 215) are formed inclined to the direction of rotation of the rotary shaft from the vicinity of an outer-diameter-side end portion of the communication groove, and wherein the supply grooves (13, 113, 213) are open on a sealed fluid side of the seal ring and extending in a radially outward direction toward inner diameter sides of the inclined grooves (15, 115, 215).