A separation mechanism of a fixing device includes a separation member extending in a direction orthogonal to the paper convey direction and arranged opposite the fixing member in a state apart from the fixing member by a predetermined gap, a support shaft member extending in a direction orthogonal to the paper convey direction and rotatably supporting the separation member, a first gap adjustment unit capable of rotating the separation member around the support shaft member to adjust the predetermined gap in the rotation direction, and a second gap adjustment unit capable of moving the separation member in a direction in which an imaginary surface from the support shaft member towards the fixing member extends, to adjust the predetermined gap in the surface direction.