A manufacturing method of a speaker diaphragm where a speaker diagram (30, 40, 50, 60, 70) is manufactured from a piece of wooden sheet, comprising: a lubricant impregnating step (c) of wetting and softening the wooden sheet, and impregnating a lubricant which acts to keep water in the wooden sheet; a first pressing step (d) of tentatively molding the wooden sheet in a predetermined shape; a first drying step (e) of drying the wooden sheet tentatively molded in the predetermined shape; a thermosetting resin impregnating step (f) of impregnating thermosetting resin into the wooden sheet dried in the first drying step (e); a half-drying step (g) of half-drying the wooden sheet impregnated with the thermosetting resin; a second pressing step (h) of molding the wooden sheet half-dried in the half-drying step (g) in a predetermined shape by heating and pressing; characterized in that the lubricant being an aqueous solution including at least one of saccharides, glycerine and amino acids, further comprising: a release agent impregnating step of impregnating a release agent into the wooden sheet; a second drying step of drying the wooden sheet impregnated with the release agent; and a third pressing step of heating and pressing the wooden sheet dried in the second drying step to mold in a predetermined shape; and a moisture-proof agent applying step of applying a moisture-proof agent to the wooden sheet molded in the predetermined shape; the release agent impregnating step, the second drying step, and the third pressing step being provided between the second pressing step and the moisture-proof agent applying step. a lubricant impregnating step (c) of wetting and softening the wooden sheet, and impregnating a lubricant which acts to keep water in the wooden sheet; a first pressing step (d) of tentatively molding the wooden sheet in a predetermined shape; a first drying step (e) of drying the wooden sheet tentatively molded in the predetermined shape; a thermosetting resin impregnating step (f) of impregnating thermosetting resin into the wooden sheet dried in the first drying step (e); a half-drying step (g) of half-drying the wooden sheet impregnated with the thermosetting resin; a second pressing step (h) of molding the wooden sheet half-dried in the half-drying step (g) in a predetermined shape by heating and pressing; characterized in that the lubricant being an aqueous solution including at least one of saccharides, glycerine and amino acids, further comprising: a release agent impregnating step of impregnating a release agent into the wooden sheet; a second drying step of drying the wooden sheet impregnated with the release agent; and a third pressing step of heating and pressing the wooden sheet dried in the second drying step to mold in a predetermined shape; and a release agent impregnating step of impregnating a release agent into the wooden sheet; a second drying step of drying the wooden sheet impregnated with the release agent; and a third pressing step of heating and pressing the wooden sheet dried in the second drying step to mold in a predetermined shape; and a moisture-proof agent applying step of applying a moisture-proof agent to the wooden sheet molded in the predetermined shape; the release agent impregnating step, the second drying step, and the third pressing step being provided between the second pressing step and the moisture-proof agent applying step.