The combustion zone propagating through an iron particle cloud and the combustion behavior of individual iron panicles have been examined by using high-speed photomicrographs. Propagation of the combustion zone of 4˜5 mm in width was observed as the movement of a luminous zone which consists of burning iron particles. In the region just behind the leading edge, burning particles of various diameters are examined. As the distance from the leading edge becomes larger, smaller particles are fading away, and then only large particles are observed to remain luminous in the region where the distance is larger than 2 mm. Each iron particle bums at the combustion zone without gas phase flame. The burn-out time (the duration of light emission) is proportional to the diameter of iron particle when the particle diameter is not so large. It agrees well with the result of a simple analysis. As the particle diameter becomes larger, the burn-out time becomes much larger than that predicted by the simple analysis.