A series of experiments was performed to clarify the unique time structure in Zen. As a result, subjective time became longer during Zazen, and those factors for underestimation of time were provided in terms of all conditions, including environmental, physiological and subjective. This tendency toward underestimation of time during Zazen appears to realize a relation between Muga (Non-Ego) and Muji (No-Time) in Zen Buddhism. However, Mugs in Zen Buddhism does not mean a complete absence of consciousness but an unfettered, free self, that Muji does not mean the time that binds us, and that time, also, like all existences or beings, is not reality but relative, that is Ku. In conclusion, experimental problems and prospects in future were discussed.