In this paper, the probability density function of renewal of the equipment in use is shown by dividing the probability density of renewal by the physical service life and that by the economically optimum service life. These differ in the method of renewal assessment, and this category is important in practice. In addition, the probability of being updated collectively by the economically optimum life and the probability density of the update based on the physical service life after the update are shown separately. These life cycle perspectives are intended to provide the basis for FM and building maintenance planning.
