Crown top expansion is an important process for continuous development of canopy tree crowns due to increasing foliage into sunlit spaces. To understand the contribution of branch mass in the upper parts of the crowns to the expansion of crown tops, cross-sectional areas of main stems of various ages (ca. 10, 20, 30, and 40 years old) as well as the area at the crown base were investigated, in addition to shoot lengths of 2- to 7-year-old branch axes of Abies mariesii canopy trees in a subalpine forest in northern Honshu, Japan. The contribution of branch mass to shoot length along the branch axis at each branch age was examined using generalized linear models, using explanatory variables of branch mass indicators in various parts or the whole of crown. Among the models for each 4- to 7-year-old branch axis, the best explanatory variable was the indicator of branch mass from 1- to ca. 30-year-old branches. This finding suggests that not only branches near the crown top but also those nearly 30 years old contribute to the expansion of canopy tree crown tops.