Abstract. We perform 3D numerical simulations for merger of equal mass binary neutron stars in full general relativity preparing irrotational binary neutron stars in a quasiequilibrium state as initial conditions. Simulations have been carried out for a wide range of stiffness of equations of state and compactness of neutron stars, paying particular attention to the final products and gravitational waves. We take a fixed uniform grid in Cartesian coordinates with typical grid size (293, 293, 147) in (x, y, z) assuming a plane symmetry with respect to the equatorial plane. A result of one new large-scale simulation performed with grid size (505, 505, 253) is also presented.We find that the final product depends sensitively on the initial compactness of the neutron stars: In a merger between sufficiently compact neutron stars, a black hole is formed in a dynamical timescale. As the compactness is decreased, the formation timescale becomes longer and longer. For less compact cases, a differentially rotating massive neutron star is formed instead of a black hole. In the case of black hole formation, the disk mass around the black hole appears to be smaller than 1% of the total rest mass. It is also indicated that waveforms of high-frequency gravitational waves after merger depend strongly on the compactness of neutron stars.