To provide a deformation absorbing member capable of suppressing the volume variation of cooling water between an anode side separator and a cathode side separator for ensuring good circulation of a fuel cell (1), a deformation absorbing member (30) is proposed which is used by being stacked between an anode side separator (11) and a cathode side separator (12) assembled in pairs to absorb each of the deformations of the stacked members, including, for example, a separator unit (10) consisting of the anode side separator and the cathode side separator and a membrane electrode assembly (20). The deformation absorbing member includes an absorbing portion for absorbing variation in the in-plane distribution of stress caused by deformation along the stacking direction (X) of the stacked members.