An experimental investigation of flashback was conducted during the start-up of a practical premixed kerosene burner. The flame propagations for normal ignition and flashback were visualized with high time-resolution. The timing of the fuel supply and ignition, as well as time sequence variations in pressures and temperatures in the burner, were analyzed to clarify the phenomena. The accumulated data revealed that flashback was caused by reverse flow of the hot combustion products through the flashback arrester and that the probability of flash back increased with increasing ignition delay, due to the higher pressures resulting from ignition and burning of the fuel accumulated in the combustion chamber during the delay. The thermal energy passing through the perforated plate used for flame quenching between the combustion chamber and the evaporating chamber was estimated using the reverse-flow pressures and their periods. The ignition energy estimated for the kerosene vapor mixtures was of the order of 10 mJ, which corresponds to the minimum ignition energy of other hydrocarbon fuels.