A flap valve mechanism in an open-close device for fuel tank includes an open-close member, a shaft support mechanism, a spring and a gasket. The shaft support mechanism includes bearing members and a rotation restricting mechanism. The rotation restricting mechanism includes restricting elements and restricted elements to be engaged with the restricting elements. At a first position, the restricting elements are engaged with the restricted elements, so that the open-close member is moved in a direction of warping the gasket. At a second position, the restricting elements are disengaged from the restricted elements, so that the open-close member is rotated about shaft members.