In-situ stress measurements using the hydraulic fracturing technique have been made at about ten points in the Kanto-Tokai area in these five years to get knowledge about stress condition in the area. The Nakaminato site is one of those measurement points, which is in the northeastern corner of the Kanto Plain. A well of 450m depth is drilled at the Nakaminato site through siltstone of the Upper Cretaceous which is narrowly exposed along the coastline. Nine sets of stresses were obtained successfully below the depth of 200m in the well. Data show that the maximum and the minium horizontal compressive stresses, S_Hmax and S_Hmin increase almost linearly with depth, and are represented by
S_Hmax=0.43h+1.2
S_Hmin=0.24h+10.4
S_V=0.23h
where stresses are in bars, h is the depth in m and S_V is the vertical stress calculated from density log data. Both an ultrasonic borehole televiewer and an impression packer are used for detecting the azimuth of S_Hmax which is known from the orientation of the hydraulic fractures on the well wall. The direction of S_Hmax is observed as N50°E±20°. The direction dose not agree well with that estimated from the relative westward motion of the Pacific plate to the Eurasian plate: E-W.