A cell cultivation carrier implantable in vivo having independent pore with opening of 100 μm-1000 μm on the surface thereof produced by neutralization•gellation of collagen acidic solution, said collagen acidic solution is preliminary prepared by passing through a filter of 10 μm or less pore size by 5-20 mg/mL concentration. Especially, a cell cultivation carrier implantable in vivo having sufficiently self-organized accumulation shape•structure obtained by carrying out said neutralization under directionally supplying of alkali.