jigs of good gas permeability disposed on the upper and lower sides of the laminated body when there are electrode layers inside the laminated body diffusion of the atmosphere is blocked and a difference in the diffusion of the atmosphere from the surfaces parallel to the electrode upper and lower surfaces is likely to occur between the region lying in a few layers from the upper and lower surfaces and other region leading to a fluctuation of characteristics it is also desirable in the sintering step to place the laminated body in the sagger with a weight disposed on it in order to suppress deformation of the sheet however since the weight and the sagger act to shield the laminated body from the atmosphere the atmosphere does not sufficiently diffuse into the upper and lower surfaces directly in contact with these shields thus deformation tends to occur between the central region and the region of a few upper and lower layers therefore in the sintering step for example the laminated body is preferably sandwiched between aerating boards disposed on the upper and lower surfaces of the body and spacer layers of good gas permeability are provided on the outside in order to distribute the atmosphere evenly over the upper and lower surfaces of the laminated body the aerating board directly in contact with the laminated body is preferably formed of materials having no reactivity with the laminated body in this manner a difference in the distribution of atmosphere between the region of the upper and lower surfaces of the laminated body and the central region where the atmosphere diffuses from the sides can be reduced deformation due to difference in the distribution of the atmosphere is thereby suppressed and a difference between the diffusion of the atmosphere from the.