This paper describes the characteristics of flame motion in the throat of a swirl- chamber diesel engine. Two optical-fiber probes were installed in a cylinder head to transmit the radiant light from a flame passing two halfway locations in the throat. The radiant light intensity from the probe was converted into an electric signal (a flame signal) by a photoelectric transducer. The temporal phase difference between two flame signals was measured at each crank angle by the correlation between feature points on both signals. From these results, transitions of the moving velocity of a flame in the throat were obtained. Immediately after the flame begins to spout into the main chamber, the moving velocity of the flame in the throat gradually decreases to a minimum. Then the velocity increases to a maximum, and decreases again as combustion proceeds. There is a correlation between transitions of the moving velocity of a flame and heat release rate in the middle and final stages of the combustion.