A chronological table which is composed of columns of a gas-liquid two-phase flow research, formulae of critical heat flux in boiling heat transfer, progress of type of boilers, and type of heat transfer, progress of type of boilers, and type of nuclear reactors is presented. The relationship between the development of the two-phase flow and heat transfer researches and the related technology of boilers and nuclear reactors is discussed based on the chronological table. A historical aspect of the development of the two-phase flow research is described. The progress of the research is divided by four stages according to the feature of the researches in each stage. These periods are 1948-1959, 1960-1970, 1971-1979, and 1980-1988. In this first report are described an intension of the aurthor's research on the two-phase flow which was started in 1948, the progress of the two-phase flow researches in the first period, and also the state of electric power generation capacity at that period in Japan as a background for the development of the two-phase flow research.