To provide solid soap effectively utilizing shrinking solid soap remained.

A soap substrate originally including more water than usual is solidified to become solid soap easily deformable by hands and having flexibility to the level of clay. The solidified soap is sandwiched between shrinking and old solid soap and new and big solid soap, adhered to both of them, and pressurized by hands, thereby deforming itself and filling the gaps between the soap. Thus, they are completely joined as one piece of solid soap. Although separation tends to occur immediately after joining, one piece of firm solid soap is produced by drying for one to several days to evaporate moisture content and to facilitate hardening.