  We have performed electrical resistivity measurements on single crystal
BaFe2As2 under high pressure P up to 16 GPa with a cubic anvil apparatus, and
up to 3 GPa with a modified Bridgman anvil cell. The samples were obtained from
the same batch, which was grown with a self-flux method. A cubic anvil
apparatus provides highly hydrostatic pressure, and a modified Bridgman anvil
cell, which contains liquid pressure transmitting medium, provides quasi
hydrostatic pressure. For highly hydrostatic pressure, the crystal phase and
magnetic transition temperature decreases robustly with P and disappears at
around 10 GPa. The superconducting phase appears adjacent to magnetic phase in
narrow pressure region between 11 and 14 GPa. The tiny difference of
hydrostaticity between the cubic anvil apparatus and modified Bridgman anvil
cell induces a drastic effect on the phase diagram of BaFe2As2. This result
indicates that small uniaxial stress along c-axis strongly suppresses the
structural/antiferromagnetic ordering and stabilizes superconductivity at much
lower pressure.
