The local density of states (LDOS) around an impurity or surface, which can be observed in scanning tunneling spectroscopy, is studied in the two-dimensional t-t'-J model. The spatial dependence of the order parameter is numerically determined self-consistently using the Gutzwiller approximation and the Bogoliubov-de Gennes theory. It is found that the LDOS shows the zero-energy peak when the t' term exists.