Abstract: This study aims to explore the current “double ageing” (demographic ageing of residents and physical ageing of facilities) in high-rise (over 20 stories by the Japanese Government’s definition) residential buildings in Tokyo, where the rate of ageing has increased most rapidly since the late 1990s, compared to those of other cities and high-rise residential buildings worldwide. First, the trend of demographic ageing in the districts where high-rise residential buildings are concentrated is analysed. The results show that demographic ageing in high-rise residential buildings is faster than in other residential buildings because the age group of the residents is concentrated across two generations: the generation born in 1946–1955 and the generation born in 1966–75. Second, the relationship between demographic and physical ageing was examined through an online survey of 978 residents of high-rise residential buildings conducted in January 2021. A generation gap in values regarding their high-rise residential buildings was clearly identified. Third, the cause and result of the generation concentration and gap were investigated via an interview survey of 26 informants extracted from the online survey. Three main findings emerged: (a) the ageing of the generation born in 1946–1955 has given rise to housing insecurity because of the decline in income, (b) the high rate of singles within the generation born in 1966–1975 may be as a result of housing insecurity after their retirement, and (c) the introduction of social distancing has accelerated the substantial “ageing” of relatively good facilities, but a straightforward generational conflict was not fully deciphered in this article because of lifestyle diversification over generations and organisational culture of management associations.