In a manufacturing method, resin in a molten state which becomes a film raw material is caused to hang down from a discharge port of a discharger and the film-like film raw material is continuously discharged, a sheet is conveyed along a sheet pass line, a tip part of the film raw material is formed by cutting and removing an initially formed part of the initially formed film raw material, the tip part is overlapped on the sheet on the sheet pass line, the sheet and the film raw material in a mutually overlapping state are conveyed along the sheet pass line, and the sheet and the film raw material are introduced to a joining part from the sheet pass line.