A male coupling member is provided that is selectively couplable to a first female coupling member (for 25 MPa, for example) and a second female coupling member (for 90 MPa), which handle different fluid pressures. When the male coupling member is coupled to the first female coupling member, a second O-ring that is provided for the second female coupling member is prevented from being displaced by the fluid supplied from the first female coupling member. A through-hole (70) is provided therein with an O-ring retaining member (82) that is displaceable between an advance position