A NOx emission reduction apparatus includes high-temperature EGR gas supply means for supplying a high-temperature EGR gas into an engine cylinder, low-temperature EGR gas supply means for supplying a low-temperature EGR gas into the engine cylinder and very-low-load operation control means for, as an engine load decreases in a very-low-load range, increasing an EGR rate of the high-temperature EGR gas and decreasing an EGR rate of the low-temperature EGR gas for stable engine operations and NOx emission reduction.