To simply form gap parts in a composite material being the raw material for an electromagnetic induction heating type vessel.

Each metal layer for joining is beforehand provided on the whole face of the confronted face in a nonmagnetic metal sheet and a magnetic metal sheet, and they are set between a pair of press dies arranged so as to be confronted on both the sides in the axial direction of a hot press apparatus. At least either in the press dies is provided with step-like projecting parts of projecting toward the confronted mating press die. Upon a hot press, the respective metal sheets in the regions sandwiched between the step-like projection parts and the mating press die are formed as joints at which the metal layers for joining are integrally joined. On the other hand, the respective metal sheets in the regions not sandwiched by the projecting step parts are formed as non-joined parts to form into gap parts, thereby obtaining the composite material having the gap parts partially.