Abstract: A development monitoring apparatus in which a non-exposed wafer is easily reworked by monitoring a developed portion and an undeveloped portion of a photoresist film on a wafer. The apparatus includes a light source for outputting incident light to a wafer having a photoresist film coated with a developer, and a light collector for collecting reflected light reflecting from the wafer. A filter transmits only the reflected light having a desired wavelength. A photoelectric device transforms the reflected light which passes through the filter into an electrical signal. Correct development of the photoresist film is determined by measuring the intensity change of the electrical signal over time. Accordingly, an exposed wafer and an non-exposed wafer are rapidly reworked, so that an increase in manufacturing costs and deterioration of yield rate can be prevented.