For the stress measurement by hydrofracturing, the observed borehole pressures of Pr and Ps, i.e. the reopening and shut-in pressures, should be related independently to the maximum stress SH and the minimum stress Sh, and the independent relationships give the principle for the two values of SH and Sh to be determined from the two observations of Pr and Ps. However, the data of field tests so far indicate that the measured reopening pressure lies close to the shut-in pressure, i.e. Pr = Ps, are far more numerous than can reasonably be expected. To examine such a paradox, we carried out field tests of hydrofracturing, and then we confirmed that borehole pressure is fairly influenced by the hydraulic compliance of test equipments, C, as expected from our theoretical model which has been developed so far. The model suggests that if the C will be reduced small enough, then the measured reopening pressure Pr (a) approaches the true reopening pressure, Pr0, i.e. the borehole pressure at which the fracture truly begins to open from its mouth at the borehole wall. Thus we could measure Pr0 approximately from Pr (a) by using stiff hydrofracturing system. The detected Pr0 allows us to estimate SH on condition that the magnitude of Sh is known from the shut-in pressure.