The disclosed invention relates to a fluid reforming tube comprising: a tubular case having an accommodation space therein; an inlet port provided on the upstream side between both ends of the case; an outlet port provided on the downstream side; an energy applying portion which is tightly fixed to the inner circumference of the case and is formed by stacking a plurality of meshes along a direction in which a fluid introduced in the case flows; and a magnetic substance provided in the accommodation space of the case and disposed on at least one of the upstream and downstream sides of the energy applying portion, wherein, in the mesh, hexagonal ribs form borders between sieves, and the cross-sectional shape of the sieve along the flow direction of the fluid introduced into the case has an hourglass shape with a neck, in which the middle portion is narrowed due to the rib therein.