Recently, in order to clarify earth pressure phenomena, the stress in rock has been frequently measured by stress relief technique. The measured stress, however, is the-disturbed stress by the opening in which the measuring apparatus is placed. As it is supposed that the knowledge of the original stress, the stress that, would exist if the opening were not made, will be helpful to the investigation of earth pressure phenomena, the authors have studied theoretically the method to find the original stress. It is found that the measurements of principal stress at more than three points on the wall surface of a drift or the measurements of deformation of a bore hole in more than six directions enable to determine the original state of stress The detailed method of calculation with an example of its application are suggested in this paper.