The trajectories of maximum horizontal tectonic stress in the Japanese Islands are inferred from Quaternary tectonic movements based on geological and geomorphological investigations, present-day crustal movements obtained by geodetic surveys, and earthquake focal mechanisms etc. Tectonically active regions can also be predicted from the rate of crustal strain variation. The earth's crust, however, is not a homogeneous, isotropic, elastic solid, but exhibits various types of non-elastic behaviour . The geological structure of the Islands is very complicated and there are many active faults and folds . Therefore, high rates of strain variation observed in geodetic surveys do not always indicate large accumulations of strain energy in the crust, particularly in the Island Arc. Absolute stress magnitudes in the crust are required to define these values . For the investigation of crustal deformations, it is very important to clarify the stress state in the uppermost crust, especially three dimensionally . In some regions, the directions of principal stress obtained by focal mechanism solution of shallow earthquakes do not always agree with those of principal strains by geodetic surveys . Moreover, sometimes one of the principal stresses in the top layer of the crust is not vertical . This situation occurs characteristically in the tectonically active, and topographically steep, Islands.