This article explains lithic assemblage transitions during the Early Upper Palaeolithic (EUP) on the Musashino Upland by quantitative comparisons of lithic raw materials, core reduction (blade technology), and formal tool production. The results suggest that changes in aspects of lithic assemblage variability could be explained by changes in raw material utilization, not developments (sophistication of tool-making skills) in blade technology and methods of formal tool production. The results also indicate the possibility that the changes in lithic raw material would have been affected by changes in residential mobility and the foraging territorial scale of EUP hunter-gatherers, as well as the changes in organic raw material utilization in whole technological organization in various environmental settings during the EUP. Beside them, the characteristics of the lithic assemblages in Period I as the initial EUP assemblages in this region are different from general characteristics of Upper Palaeolithic assemblages (blade technology, standardized and formal flaked tools) in Eurasia. The nature of lithic raw material utilization, especially flaked tool use, in Period I assemblages looks extremely expedient. Therefore, the characteristics of initial EUP assemblages in this region represent that diversity in lithic raw material utilization and technological organization was present during the EUP.