PURPOSE: To form the section in different forms at the left side and the right side, and the upper side and the lower side respectively, and to prevent a minute rotation and a deterioration of a seal ring, by forming a slit having an opening on one side surface of the seal ring, and forming an angle form curved surface on one side piece of both side pieces opposing at both sides of the slit.

CONSTITUTION: While a seal ring 1 is formed in a ring form, it has a contact to an opponent surface. In this case, in the section form of the seal ring 1, on one surface of three surfaces to form the profile, a slit 2 having an opening 2a is formed. And to the opposite side of the surface of one side piece 3 corresponding to the slit 2, contacting to an opponent surface, of both side pieces 3 and 4 opposing at both sides of the slit 2, an angle form curved surface 5 curved in an angle form so as to separate from the slit 2 is formed. When the seal ring is used, the seal ring 1 is set to a setting groove 11 formed on the outer surface of a slide body 10 sliding inside a tubular body 9. As a result, the angle form curved surface 5 on one side piece 3 is contacted to the inner peripheral surface 9a of the tubular body 9, so as to accomplish the sealing purpose.