  The two-dimensional t-J model on a frustrating lattice is studied using
mean-field variational theories with Gutzwiller approximation. We find that a
superconducting state with broken time-reversal symmetry (d+id state) is
realized in the parameter region close to the triangular lattice. The
frustration enlarges the region of superconductivity when $t<0$ for the
hole-doped case, which is equivalent to $t>0$ for electron doping. We also
discuss the SU(2) degeneracy at half-filling. The d+id state probably
corresponds to the spin gap state at half-filling.
