A fuel treatment device in which a fuel gas is supplied to a catalyst to produce a reformed gas, the catalyst filling a catalyst filling space which is surrounded by a cylindrical outer circumferential wall or by a cylindrical inner circumferential wall and the cylindrical outer circumferential wall, the catalyst filling space being disposed along a center axis of the cylinder, the device comprising: an oval annular shallow groove serving as a removal section indicator (30, 38) indicating a position of a catalyst removal section which is to be opened for removing the catalyst from the catalyst filling space through the opened catalyst removal section, the catalyst removal section being placed on the cylindrical outer circumferential wall, and the removal section indicator being placed on an outer surface of the cylindrical outer circumferential wall, wherein the catalyst removal section can be cut off from the cylindrical outer circumferential wall, or the cylindrical outer circumferential wall can be cut off at the catalyst removal section, characterized in that: in that the oval annular shallow groove further serves as an opening formation assister for assisting formation of a catalyst removal opening in the catalyst removal section, wherein the oval annular shallow groove has a depth of 1/5 to 1/20 of the thickness of the cylindrical outer circumferential wall, and the oval annular shallow groove and the catalyst removal section are provided over the entire length in the axial direction of the catalyst filling space, and by a catalyst indicator that indicates the kind of the catalyst, and further comprising one or more shelf plates which divide the catalyst filling space into two or more regions arranged in the axial direction, the shelf plate being formed without being fixed to the outer circumferential wall surrounding the catalyst filling space being fixed to the inner circumferential wall surrounding the catalyst filling space, and having a curved portion formed at the inner circumferential position, and further comprising a protrusion on the outer circumferential surface of the cylindrical outer circumferential wall, wherein the protrusion can be cut off in a manner that a hook hole is formed in the the cylindrical outer circumferential wall. an oval annular shallow groove serving as a removal section indicator (30, 38) indicating a position of a catalyst removal section which is to be opened for removing the catalyst from the catalyst filling space through the opened catalyst removal section, the catalyst removal section being placed on the cylindrical outer circumferential wall, and the removal section indicator being placed on an outer surface of the cylindrical outer circumferential wall, wherein the catalyst removal section can be cut off from the cylindrical outer circumferential wall, or the cylindrical outer circumferential wall can be cut off at the catalyst removal section, characterized in that: in that the oval annular shallow groove further serves as an opening formation assister for assisting formation of a catalyst removal opening in the catalyst removal section, wherein the oval annular shallow groove has a depth of 1/5 to 1/20 of the thickness of the cylindrical outer circumferential wall, and the oval annular shallow groove and the catalyst removal section are provided over the entire length in the axial direction of the catalyst filling space, and by a catalyst indicator that indicates the kind of the catalyst, and further comprising one or more shelf plates which divide the catalyst filling space into two or more regions arranged in the axial direction, the shelf plate being formed without being fixed to the outer circumferential wall surrounding the catalyst filling space being fixed to the inner circumferential wall surrounding the catalyst filling space, and having a curved portion formed at the inner circumferential position, and further comprising a protrusion on the outer circumferential surface of the cylindrical outer circumferential wall, wherein the protrusion can be cut off in a manner that a hook hole is formed in the the cylindrical outer circumferential wall. in that the oval annular shallow groove further serves as an opening formation assister for assisting formation of a catalyst removal opening in the catalyst removal section, wherein the oval annular shallow groove has a depth of 1/5 to 1/20 of the thickness of the cylindrical outer circumferential wall, and the oval annular shallow groove and the catalyst removal section are provided over the entire length in the axial direction of the catalyst filling space, and by a catalyst indicator that indicates the kind of the catalyst, and further comprising one or more shelf plates which divide the catalyst filling space into two or more regions arranged in the axial direction, the shelf plate being formed without being fixed to the outer circumferential wall surrounding the catalyst filling space being fixed to the inner circumferential wall surrounding the catalyst filling space, and having a curved portion formed at the inner circumferential position, and further comprising a protrusion on the outer circumferential surface of the cylindrical outer circumferential wall, wherein the protrusion can be cut off in a manner that a hook hole is formed in the the cylindrical outer circumferential wall.