The shaft seal apparatus is comprised of a first sealing portion, a second sealing portion, a first
backup diaphragm and an engagement ring, wherein the first sealing portion has a fit
mount portion, a first sealing lip and a reinforcement ring, in which the fit
mount portion is retained sealingly in the seal housing side, in which an inner circumferential surface of the first sealing lip sealingly fits against the outer circumferential surface of the shaft for providing a seal against the pressurized fluid, in which the reinforcement ring has a reinforcement portion, a cylindrical portion and a joint portion, the reinforcement portion provides a reinforcement against the fit
mount portion side of the first sealing lip, the cylindrical portion is integrally joined with the fit mount portion, the joint portion is disposed in the other end of the cylindrical portion, wherein the second sealing portion has a support portion and a second sealing lip, in which the second sealing portion is made of a resin material, the support portion is in tight contact against the first sealing portion by the opposite side relative to the pressurized fluid, the support portion is arranged in parallel to the first sealing portion, wherein the first
backup diaphragm is supported by the reinforcement ring or an engagement ring which retains the support portion of the second sealing portion, wherein the engagement ring has a fitting portion, a first engagement portion and a second engagement portion in which the fitting portion fits in the bore surface of the seal housing, the first engagement portion engages against the end face of the seal housing, the second engagement portion allows the first engagement portion to support the reinforcement ring, wherein a seal is disposed between the contact surfaces of the engagement ring and the bore surface and the radial thickness of the seal is arranged smaller than the reinforcement ring or the engagement ring.