We have developed an effective interaction for shell model calculations in the model space consisting of four orbits 1p3/2, 0f5/2, 1p1/2 and 0g9/2. Starting from a renormalized Gmatrix interaction, we have modified 45 linear combinations of Hamiltonian parameters by fitting to 400 experimental binding and excitation energy data out of 87 nuclei with masses A = 63–96. The resultant effective interaction is shown to be successful for describing irregular behavior of the 0+2states in Ge isotopes. We have evaluated the two-neutrino double-beta-decay matrix elements for 76Ge and 82Se which are in reasonable agreement with the experimental data.