Rebuilding a bone with a defect by activation of the innate self regeneration ability of the bone requires a considerably long period of time. The purpose of the present invention is to provide a bone defect filling material that initiates a bone rebuilding action as quickly as possible following implantation and that afterward remains in the defect and continues acting to promote bone formation activity until sufficient bone formation has been achieved for the rebuilding of the defect. The present invention provides a cotton like bone defect filling material comprising biodegradable fibers produced by electrospinning wherein the biodegradable fibers contain 40 60 wt% of calcium phosphate particles and 10 wt% or more of silicon eluting calcium carbonate particles with the remainder containing 30 wt% or more of poly(L lactic acid) resin and the amount of the poly(L lactic acid) resin that is non crystalline is 75 98%.
