The winter range utilization pattern of a Japanese macaque troop in a snowy habitat was studied. The vegetation areas essential for subsistence were found to be relatively undisturbed mixed and deciduous forests. The concept of essential resource area (ERA) is defined. Our comparison among three troops in the same habitat in the past and present with different population densities indicated that the per capita ERA is quite important in determining the range area. This implies that the population and range area are resource-correlated.