A method for bonding metal bodies, the method comprising: preparing a first material to be bonded, the first material to be bonded being formed from a metal and having a processed layer subjected to a processing for creating atomic vacancies and/or dislocations; supplying fine metal particles between the processed layer of the first material to be bonded and a second material to be bonded; and bonding the first material to be bonded and the second material to be bonded by means of the fine metal particles, wherein the process for creating atomic vacancies and/or dislocations is mechanical processing or radiation damage by irradiation with particle beams; a Vickers hardness number of the processed layer is higher by Hv 50 or more than a Vickers hardness number of the metal before processing, the Vickers hardness number of the processed layer is from Hv 80 to Hv 120, wherein the Vickers hardness number of the processed layer can be checked by the Vickers hardness test of JIS Z 2244, in case in which the layer is less than 1 μm thick by nanoindentation; a thickness of the processed layer is 0.5 μm or more; the first material to be bonded is formed from copper or a copper alloy, silver plating or gold plating; fine metal particles are fine particles of one element selected from a metal element group consisting of silver, gold, copper, aluminum, nickel, platinum, tin, antimony and palladium, fine particles formed by mixing two or more kinds selected from the metal element group; fine particles formed from an alloy of two or more elements selected from the metal element group; fine particles obtained by mixing fine particles of one element selected from the metal element group or fine particles formed by mixing two or more kinds selected from the metal element group, with fine particles formed from an alloy of two or more elements selected from the metal element group; or an oxide thereof, the processed layer of the first material to be bonded is recrystallized by heating the first material to be bonded, to a temperature higher than or equal to the recrystallization temperature of the processed layer of the first material to be bonded. preparing a first material to be bonded, the first material to be bonded being formed from a metal and having a processed layer subjected to a processing for creating atomic vacancies and/or dislocations; supplying fine metal particles between the processed layer of the first material to be bonded and a second material to be bonded; and bonding the first material to be bonded and the second material to be bonded by means of the fine metal particles, wherein the process for creating atomic vacancies and/or dislocations is mechanical processing or radiation damage by irradiation with particle beams; a Vickers hardness number of the processed layer is higher by Hv 50 or more than a Vickers hardness number of the metal before processing, the Vickers hardness number of the processed layer is from Hv 80 to Hv 120, wherein the Vickers hardness number of the processed layer can be checked by the Vickers hardness test of JIS Z 2244, in case in which the layer is less than 1 μm thick by nanoindentation; a thickness of the processed layer is 0.5 μm or more; the first material to be bonded is formed from copper or a copper alloy, silver plating or gold plating; fine metal particles are fine particles of one element selected from a metal element group consisting of silver, gold, copper, aluminum, nickel, platinum, tin, antimony and palladium, fine particles formed by mixing two or more kinds selected from the metal element group; fine particles formed from an alloy of two or more elements selected from the metal element group; fine particles obtained by mixing fine particles of one element selected from the metal element group or fine particles formed by mixing two or more kinds selected from the metal element group, with fine particles formed from an alloy of two or more elements selected from the metal element group; or an oxide thereof, the processed layer of the first material to be bonded is recrystallized by heating the first material to be bonded, to a temperature higher than or equal to the recrystallization temperature of the processed layer of the first material to be bonded.