Dynamic processes of the step bunching on a Si(001) vicinal surface during Au deposition were studied by using reflection electron microscopy. During the growth of the Si(001) 5×3.2-Au terraces, the step bunching occurs and the evolution of the terrace width is fitted in a form of t^a with respect to time t for temperature between 780 and 900°C. The exponent α is 1/4 at 820°C, increases gradually with temperature and is 1/2 above 870°C. This suggests that step bunching kinetics changes with temperature. It was found that the kinetics is governed by surface diffusion in low temperature region and by evaporation in high temperature region. Dynamic processes during debunching were also analyzed in the same way. Time evolution of terrace width can be fitted by a function of A^* (to-t)^α'. It is unity below 820°C and decreases with increasing substrate temperature to reach to 1/2 above 870°C. This suggests that mass transport kinetics changes with temperature and the transport of Au is the rate determining process below 820 °C.