A nitrogen gas tank, a rotary pump and a mechanical booster pump are connected to a bonding vessel that constitutes a bonding apparatus for carrying out diffusion bonding, the apparatus further comprising a pressure sensor. A nitrogen gas atmosphere is formed inside the bonding vessel, and under control operations of a control circuit, a nitrogen introduction rate is controlled so that a pressure is substantially fixed at a predetermined pressure between 3-105 Pa. At such a state, under the action of a rod of a hydraulic cylinder, a second electrode is brought into proximity with a first electrode, so that ultimately, a first object to be bonded and a second object to be bonded on the first electrode are pressed. Further, current is applied through the first electrode and the second electrode with respect to the first object to be bonded and the second object to be bonded.