A fixing device comprising: a flexible tubular member that is circularly movable in a moving direction and has an inner peripheral surface; a nip member disposed so as to be in sliding contact with the inner surface of the tubular member; a backup member configured to provide a nip region in cooperation with the nip member upon nipping the tubular member between the backup member and the nip member; and a leaf spring member that is disposed so as to be in sliding contact with the inner peripheral surface of the tubular member and is configured to urge the inner peripheral surface of the tubular member outward in a radial direction of the tubular member and wherein the tubular member has axial end portions in an axial direction, and further comprising a pair of guide members each of which is located on corresponding one of the axial end portions of the tubular member, each of the pair of guide members having a guide surface that is configured to be in sliding contact with the inner peripheral surface of the tubular member to guide a circular movement of the tubular member, and wherein the leaf spring member comprises a pair of leaf spring members each of which is positioned on corresponding one of the axial end portions of the tubular member, each of the pair of leaf spring members including an arm portion that extends in a circumferential direction of the tubular member and has an end portion positioned downstream in the moving direction, the end portion of the arm portion being configured to be in sliding contact with the inner peripheral surface of the tubular member, and wherein each of the leaf spring members is disposed such that the arm portion overlaps with the guide surface in the axial direction of the tubular member, further comprising a single attaching member that is located inside the tubular member and that extends in the axial direction, and a stay that is located inside the tubular member and supports the nip member, thereby being configured to receive a load from the backup member, the attaching member is fixed to the stay, wherein each of the pair of leaf spring members further includes a base portion fixed to the attaching member, each of the arm portions extending from each of the base portions in the moving direction, each of the arm portions being resiliently deformable upon contact of the end portions with the inner peripheral surface of the tubular member, the end portion of each of the arm portions being positioned downstream in the moving direction relative to each of the base portions. a flexible tubular member that is circularly movable in a moving direction and has an inner peripheral surface; a nip member disposed so as to be in sliding contact with the inner surface of the tubular member; a backup member configured to provide a nip region in cooperation with the nip member upon nipping the tubular member between the backup member and the nip member; and a leaf spring member that is disposed so as to be in sliding contact with the inner peripheral surface of the tubular member and is configured to urge the inner peripheral surface of the tubular member outward in a radial direction of the tubular member and wherein the tubular member has axial end portions in an axial direction, and further comprising a pair of guide members each of which is located on corresponding one of the axial end portions of the tubular member, each of the pair of guide members having a guide surface that is configured to be in sliding contact with the inner peripheral surface of the tubular member to guide a circular movement of the tubular member, and wherein the leaf spring member comprises a pair of leaf spring members each of which is positioned on corresponding one of the axial end portions of the tubular member, each of the pair of leaf spring members including an arm portion that extends in a circumferential direction of the tubular member and has an end portion positioned downstream in the moving direction, the end portion of the arm portion being configured to be in sliding contact with the inner peripheral surface of the tubular member, and wherein each of the leaf spring members is disposed such that the arm portion overlaps with the guide surface in the axial direction of the tubular member, further comprising a single attaching member that is located inside the tubular member and that extends in the axial direction, and a stay that is located inside the tubular member and supports the nip member, thereby being configured to receive a load from the backup member, the attaching member is fixed to the stay, wherein each of the pair of leaf spring members further includes a base portion fixed to the attaching member, each of the arm portions extending from each of the base portions in the moving direction, each of the arm portions being resiliently deformable upon contact of the end portions with the inner peripheral surface of the tubular member, the end portion of each of the arm portions being positioned downstream in the moving direction relative to each of the base portions.