Under experimentally controlled condition, population of the azuki bean weevil, Callosobruchus chinensis was subjected to be attacked by the parasite, Neocatolaccus mamezophagus. It is the main point of the present work to verify experimentally whether or not the balance of interacting system of host and its parasite exists when the density independent immigration, such as artificial adding of constant percentage, has an influence upon the host-parasite interacting system. The interacting population was maintained in the laboratory at 30℃ and 75% R.H. being supplied with constant amount of azuki beans as food in each generation. And a fixed number of both host and parasite population or host population or parasite population which is a certain percentage of control population was added to the original population of host-parasite system in every generation, and it was observed how the steady state was altered by these treatments. The methods of adding are as follows : Host was added during the first 6 days of host emergence. Host is full-grown larva on the 14th day after host oviposition, and parasite can easily lay its eggs in the host from outside the bean. Parasite was added for 4 days from 12th day after host oviposition. In all experiments, percentages of such adding of host or parasite population as mentioned above were 25,50,75 per cent of the control population. In any case of the adding, host-parasite system maintains a steady level of population density, but the steady state of each adding population changes its level from that of the non-adding population(as is shown in Table 2). When parasites were introduced into the population, the steady state moved to another density. This displacement of the steady density may be varied by the action of parasite. Neocatolaccus is a parasite attacking the full-grown larvae of the hosts and is unable to have an influence directly on the host population. The density of parasite population depends on the initial density of host, which has a considerable relation with the final density of host in the previous generation, and the density of parasite population has also the effect on the final density of host in a generation. After these consideration as to the determination of steady state in the host-parasite interacting system, it seems that the density effect of host population plays an important role.