Disclosed is a sintered NdFeB magnet having high coercivity (H cJ ) a high maximum energy product ((BH) max ) and a high squareness ratio (SQ) even when the sintered magnet has a thickness of 5 mm or more. The sintered NdFeB magnet is produced by diffusing Dy and/or Tb in grain boundaries in a base material of the sintered NdFeB magnet by a grain boundary diffusion process. The sintered NdFeB magnet is characterized in that the amount of rare earth in a metallic state in the base material is between 12.7 and 16.0% in atomic ratio, a rare earth-rich phase continues from the surface of the base material to a depth of 2.5 mm from the surface at the grain boundaries of the base material, and the grain boundaries in which R H has been diffused by the grain boundary diffusion process reach a depth of 2.5 mm from the surface.