A manufacturing method of a fuel cell module includes: forming an outer divided body having a frame shape and formed from an uncrosslinked item of solid rubber having adhesiveness in a seal member arrangement portion of a separator to produce an outer temporary assembly, and forming an inner divided body having a frame shape and formed from an uncrosslinked item of solid rubber in a peripheral edge portion of an electrode member to produce an inner temporary assembly; fitting the inner temporary assembly into a frame of the outer temporary assembly to produce a cell assembly temporary assembly; arranging a cell assembly stack, in which a plurality of the cell assembly temporary assemblies are stacked, in a forming die; and pressurizing and heating the forming die to crosslink the uncrosslinked item