In recent Japanese society, we are facing a severe increase in the number of patients who suffer from motor paralysis and other dysfunctions. Establishing an effective rehabilitation system for them is important, and the key to attain this target is to clarify the mechanisms of one's body perception in the brain. The feeling of controlling our action and external event is an important aspect of body perception, and thus is a topic we have to investigate. This feeling is called the Sense of Agency (SoA), and in order to clarify the mechanism of the SoA, it is necessary to clarify neuro-physiological indices that reflect the arising of this feeling. Recent investigated the relationship between SoA and neural activity with event-related potential (ERP) but these studies focused only on the feedback processing after the action-feedback (e.g. N100, P300), while no study investigated the neural basis of the action-preceding part during SoA paradigm. In this research we focused on feedback-anticipation as an action-preceding factor of SoA, and the purpose of this research is to find a neuro-physiological indices which reflect this factor. We hypothesized that readiness potential (RP) would reflect this factor. In the Libet's clock task based experiment, two conditions which differed in the state of the anticipations for the feedback were prepared. In order to manipulate the anticipation, the probability of the tone occurrence was manipulated in each condition. Earlier and larger RP was observed when the feedback-anticipation was inconsistent in relative with the consistent condition, and additional experiment by increasing the sample size is needed. Our study is the first one that reveals the neural basis of the action-preceding factor of SoA, and we believe that our study will contribute to unravel the neural basis of the SoA.