A rotary seal (1A,1B,1C) comprising: a core metal (2,3) including a core metal cylinder (2A,3A) having a cylindrical shape, and a core metal flange (2B,3B) extending inward in a radial direction from one end of the core metal cylinder (2A,3A) in an axial direction; and a seal member (4,5) including a base portion (4A,5A) joined to the core metal (2,3), and a seal lip portion (4B,5B), wherein the seal lip portion (4B,5B) includes a side lip protruding in a diameter-increasing manner from the base portion (4A,5A), and the side lip has an inner circumferential side surface and an outer circumferential side surface, and shapes of the inner circumferential side surface and the outer circumferential side surface that determine a thickness of the side lip are formed such that the inner circumferential side surface has a side surface shape of a cone, and the outer circumferential side surface includes a first outer circumferential portion having a side surface shape of a cone in which the thickness gradually increases from a small diameter side toward a large diameter side, and a second outer circumferential portion having a side surface shape of a cone or a column in which the thickness gradually decreases, so as to form an intermediate thick shape in which an intermediate thick portion at a boundary between the first outer circumferential portion and the second outer circumferential portion is thickest, characterized in that: a thickness of a distal end portion of the side lip is 0.5T to 0.7T, and a thickness of the intermediate thick portion is 1.2T to 1.5T, relative to a thickness T of a base end portion of the side lip, and an angle formed by a generating line of the cone of the inner circumferential side surface and a generating line of the cone or the column of the second outer circumferential portion is 10° to 30°. a core metal (2,3) including a core metal cylinder (2A,3A) having a cylindrical shape, and a core metal flange (2B,3B) extending inward in a radial direction from one end of the core metal cylinder (2A,3A) in an axial direction; and a seal member (4,5) including a base portion (4A,5A) joined to the core metal (2,3), and a seal lip portion (4B,5B), wherein the seal lip portion (4B,5B) includes a side lip protruding in a diameter-increasing manner from the base portion (4A,5A), and the side lip has an inner circumferential side surface and an outer circumferential side surface, and shapes of the inner circumferential side surface and the outer circumferential side surface that determine a thickness of the side lip are formed such that the inner circumferential side surface has a side surface shape of a cone, and the outer circumferential side surface includes a first outer circumferential portion having a side surface shape of a cone in which the thickness gradually increases from a small diameter side toward a large diameter side, and a second outer circumferential portion having a side surface shape of a cone or a column in which the thickness gradually decreases, so as to form an intermediate thick shape in which an intermediate thick portion at a boundary between the first outer circumferential portion and the second outer circumferential portion is thickest, the inner circumferential side surface has a side surface shape of a cone, and the outer circumferential side surface includes a first outer circumferential portion having a side surface shape of a cone in which the thickness gradually increases from a small diameter side toward a large diameter side, and a second outer circumferential portion having a side surface shape of a cone or a column in which the thickness gradually decreases, so as to form an intermediate thick shape in which an intermediate thick portion at a boundary between the first outer circumferential portion and the second outer circumferential portion is thickest, characterized in that: a thickness of a distal end portion of the side lip is 0.5T to 0.7T, and a thickness of the intermediate thick portion is 1.2T to 1.5T, relative to a thickness T of a base end portion of the side lip, and an angle formed by a generating line of the cone of the inner circumferential side surface and a generating line of the cone or the column of the second outer circumferential portion is 10° to 30°. a thickness of a distal end portion of the side lip is 0.5T to 0.7T, and a thickness of the intermediate thick portion is 1.2T to 1.5T, relative to a thickness T of a base end portion of the side lip, and an angle formed by a generating line of the cone of the inner circumferential side surface and a generating line of the cone or the column of the second outer circumferential portion is 10° to 30°.