PURPOSE: To increase the joining accuracy and joining strength of the metallic compound sheet for decoration by constraining the outer periphery of a multilayer material by plural members and by joining the remaining outer peripheral face of the multilayer material by diffusion with pressing it.

CONSTITUTION: The constraining member is formed by the main body 5 of the constraining member and pressure member 6. The main body 5 of the constraining member is assembled with more then two pieces of members. Plural metallic sheets (angle) having different materials of pure silver and pure copper, etc. are charged by overlapping alternately into this detachable joining container. The necessary joining pressure is given to the multilayer material by fitting a pressing member 7 into the through hole 5a of the main body 5 of the constraining member and by pinching the charged multilayer material between the space with the pressure member 6. since plates 8, 8 are inserted as well by abutting to the inner peripheral face 5c of the main body 5 of the constraining member. If necessary, an intermediate plate 9 is inserted between the pressure member 6 and pressing member 7. The necessary joining member is obtd. by raising the temp. of the inside of this container by keeping it in the prescribed vacuum and by joining with diffusion by a fixed pressure under uniform heating.