Photodissociation of NO followed by autoionization of an N atom has been studied by two-dimensional photoelectron spectroscopy using synchrotron radiation. In addition to the bands due to molecular ionization, the two-dimensional spectrum shows several characteristic patterns in the photon energy range of 21.5-27 eV which result from autoionization of the Rydberg states converging to N+(D-1(e)) into the ionic ground state N+(P-3(e)). The electronic states of the counter atomic oxygen can be determined from the lower onset energies of these patterns to be P-3(e) and/or D-1(e). Discussion is made about the transition region for the photodissociation reaction, especially being focused on the nature of the primary molecular states and their dynamical aspects including competitive molecular autoionization.