Abstract: The object of the invention is to provide a bonding method for brazing an amorphous carbon (AC) material to a metal material or a ceramic material, and to provide an electron tube device having an input/output window made of the amorphous carbon material. The surface of the amorphous carbon (AC) material is roughened to form an irregularity. A brazing material is sandwiched between the amorphous carbon material and a metal material or ceramic material. The resultant structure is heated to braze the amorphous carbon material to the metal material or ceramic material. The electron tube device includes a sealed vessel having an opening portion, a peripheral portion of which is made of a metal material or a ceramic material. The electron tube device further includes a window, made of an amorphous carbon material and bonded to the peripheral portion of the opening portion with a brazing material, and having irregularity on a surface around the opening portion.