A fixing device for thermally fixing a developing agent image to a sheet includes: a flexible tubular member having an inner peripheral surface defining an internal space; a heater; a nip member being in sliding contact with the inner peripheral surface of the flexible tubular member and having an electrically conductive surface; a stay supporting the nip member and being electrically conductive and electrically connected to the electrically conductive surface; a backup member nipping the flexible tubular member in cooperation with the nip member; a supporting member supporting the nip member and the stay, the supporting member being movable relative to the backup member; and a first grounding member disposed to be in contact with the stay for grounding the stay, the first grounding member being supported to the supporting member such that the first grounding member is integrally movable with the supporting member.