To provide a method and device for treating with plasma, capable of performing the plasma treatment uniformly to the inside of pores of a porous substrate.

This device for treating a material to be treated 4 consisting of a porous substrate with the plasma is provided by installing a plasma-generating part 1 consisting of at least a box body 11, a gas passage 12 equipped with opposing electrodes 13 and a plasma gas-discharging port 14, a roller 3 for closely adhering the material to be treated 4 consisting of the porous substrate at the plasma-discharging port 14 of the plasma-generating part 1 and a gas-supplying part 2 for supplying the gas to the plasma gas-generating part 1.