  Pressure effects on a recently discovered BiS2-based superconductor
Bi2(O,F)S2 (Tc = 5.1 K) were examined via two different methods; high pressure
resistivity measurement and high pressure annealing. The effects of these two
methods on the superconducting properties of Bi2(O,F)S2 were significantly
different although in both methods hydrostatic pressure is applied to the
sample by the cubic-anvil-type apparatus. In high pressure resistivity
measurement, Tc linearly decreased at the rate of -1.2 K GPa-1. In contrast,
the Tc of 5.1 K is maintained after high pressure annealing under 2 GPa and
470{\deg}C of optimally doped sample despite significant change of lattice
parameters. In addition, superconductivity was observed in fluorine-free Bi2OS2
after high pressure annealing. These results suggest that high pressure
annealing would cause a unique effect on physical properties of layered
compounds.
