  Spatial distributions of spontaneous magnetic fields near a surface of
cuprate high-$T_C$ superconductor YBCO with broken time-reversal symmetry are
calculated using the Ginzburg-Landau theory derived from the $t-J$ model. It is
found that the magnetic field exists in a narrow region inside the
superconductor, and it decays quickly outside the surface. Experimental
approaches possible to detect such spontaneous magnetic fields are discussed.
