Stand structure and the regeneration of Chamaecyparis pisifera on sites with and without well-developed soil in an old-growth coniferous forest, Akasawa Forest Reserve, central Japan, were investigated, along with their relationships to other important coniferous species. Of stems of C. pisifera -> 5 cm diameter at breast height, stems with intermediate size were absent in stands on the developed-soil site, while those with smaller size increased in stands on the undeveloped-soil site, which supported a higher density of C. pisifera. In the stands without recent tree-fall of canopy stems on the developed-soil site, canopy stems of C. pisifera were distributed uniformly and the understory stems, patchily. On the other hand, both canopy and understory stems of C. pisifera in stands on the undeveloped-soil site were distributed patchily. In the understory, C. pisifera occurred as clonal patches formed by vegetative reproduction on various types of microsites including bare rocks. However, the clonal patches did not occur in a stand on the developed-soil site with dense saplings of an evergreen conifer, Thujopsis dolabrata, which can expand vegetatively with a well developed soil layer. Gap formation may induce C. pisifera to develop tree-form stems from shrubby clonal patches. On developedsoil sites, C. pisifera stands that survive a long disturbance-free period on this site need catastrophic disturbance for their regeneration, which will eliminate T. dolabrata in the understory and create bare soil for colonization of C. pisifera from seeds. On undevelopedsoil sites, C. pisifera replaces itself continuously by effective vegetative reproduction. Ground instability and the wet condition of this site may promote the replacement.