a cylindrical belt having an axial direction;

a heater disposed on an inner surface of the cylindrical belt and having a longitudinal direction parallel to the axial direction;

a press roller configured to contact an outer surface of the cylindrical belt at a position opposite the heater and form a nip, the press roller being configured to rotate to convey a sheet through the nip, both longitudinal end portions of the press roller projecting by a first projection amount in a radial direction of the press roller that is more than a central portion of the press roller between the longitudinal end portions in the longitudinal direction;

a holder having a first surface supporting the heater and facing the cylindrical belt, the holder having a second surface that is opposite the first surface and has a center portion between the longitudinal end portions of the second surface projecting in a direction orthogonal to the first surface by a second projection amount that is greater than the first projection amount;

a frame configured to support the holder at both sides of the holder in a conveying direction of the sheet through the nip, the frame being on a second surface side of the holder; and

a positioning member attached to an outer surface of the frame at a position near a central portion of the frame between longitudinal end portions of the frame, a locking portion of the positioning member extending beyond the frame in a direction towards the press roller, wherein

the holder includes an engaging portion configured to engage the locking portion of the positioning member.