Nitrifying granules were applied to high-speed nitrification of wastewater discharged from an electronic industrial factory. The behavior of the formation of nitrifying granules and the start-up performance of nitrification process were examined with three types of reactors: a column with a small diameter, a column with a large diameter and a rectangular-type reactor. As a result, the performance of the three types of reactors did not give significant differences in terms of the formation of nitrifying granules and the start-up trend of the reactor. A nitrification rate of about 2.0 kgN/m³/day was achieved in all reactors.