A first seal member 50 is integrated with the surface 18a of a first metal separator 18, and is provided with a body base portion 58 having a trapezoidal-shaped cross-section and two protruded portions 60a and 60b integrated to the leading end of the body base portion 58, where said body base portion 58 is set to a height H1 for keeping a desired spring constant necessary for impact absorptions, and the protruded portions 60a and 60b are set to a height H2 for preventing the line pressure of the seal member from being abruptly changed and for keeping the strengths of the protruded portions 60a and 60b themselves.