A method of welding comprising contacting a first electrode to a porous body flow path, contacting a second electrode to a plate material, pressing the porous body flow path and the plate material by the first and second electrodes in a thickness direction of the plate material, and spot welding the porous body flow path and the plate material, wherein: a deformation of the plate material in a direction of the second electrode pressing the plate material is smaller than a deformation of the porous body flow path in a direction of the first electrode pressing the porous body flow path.