Relativity theory, which emerged in the beginning of the 20th century, was an innovative physical theory. It has its own philosophical backgrounds as well as its physical backgrounds. After Newton announced his classical mechanics in the late 17th century, philosophical problems on the nature of space and time raised. Hume suggested an empirical interpretation of space and time which is based on human perceptions, and Kant argued that space and time is a kind of recognizing form for human experience not an independent substance which exists in the external world. None-euclidean geometry, which was discovered in the first half of 19th century, made an important change in the human understanding of the nature of space and time. Riemann and Helmholtz showed that basic assumptions of geometry are a kind of empirical hypotheses, and there is a hypothesis of length measuring instrument’s behavior in the center of physical geometry. Poincare suggested that basic laws of physical geometry and physical theories are a kind of conventions not a necessary law nor an empirical fact. Mach severely criticized Newton’s concepts of absolute space and time, and he also suggested a new thought experiment against Newton’s bucket thought experiment to revive the program of making relational physics. If we want to understand the philosophical significance of the relativity theory, we have to check its philosophical backgrounds exactly.