First and second frame parts 400a and 400b support a belt guide 431 by interposing the belt guide 431 therebetween. The first frame part 400a is disposed at a downstream side of in rotation direction of a pressure roller 44 than the second frame part 400b when seeing it in a direction parallel to a rotation axis of the pressure roller 44. A convex-shaped first belt guide support part 401a for supporting the belt guide 431 is provided on a surface of the first frame part 400a, which faces the second frame part 400b. A convex-shaped second belt guide support part 401b for supporting the belt guide 431 is provided on a surface of the second frame part 400b, which faces the first frame part 400a, at a position, which is more separated from the pressure roller 44 than the first belt guide support part 401a.