A hot press for producing multilayered substrate blanks wherein the substrate blanks are placed between upper and lower bolsters via heat insulating plates and heating plates. The multilayered substrate blanks are fitted into a frame which is provided on the upper bolster and the multilayered substrate blanks are pressed and heated. The frame is fashioned of a material having a coefficient of thermal expansion less than the coefficients of thermal expansion of the multilayered substrate blanks. When the multilayered substrate blanks are pressed and heated, outside dimensions become equal to the inside dimensions of the frame. Thus, no flow of an adhesive out of the multilayered substrate blanks occurs, and as a result it is possible to produce a high density multilayered substrate with a large number of layers.