A seal ring (10) of the present invention seals operating oil hermetically and is attached to an annular seal ring groove (16) provided on an outer circumference of a shaft member (12). The seal ring (10) includes fluororesin, modified fluororesin formed by being irradiated with an ionizing radiation in a range from 1 kGy to 10 MGy inclusive in a state of being heated up to a melting point thereof or higher under an inert gas atmosphere with an oxygen partial pressure of 1.33 kPa or less, and synthetic resin having a surface energy ranging from +0 N/cm to 20˜10−5 N/cm inclusive of that of the operating oil.