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There has been a great demand for flame stability particularly in low-grade residual oil-fired burners. In order to improve the performance of the residual oil burner, it is required to obtain the stable ignition by the swirler devices which create recirculating combustion gas and rotating fuel spray flows. In the present study, a numerical simulation was made on the flow behaviors of air circulation and droplet streamlines for two types of swirlers with different angles of guide vane. A stereo PIV measurement was also made on the velocity distribution of spray droplets. One type of the swirlers is a former type called “Bent plate swirler” with a constant bending angle of the guide vanes. The air after the guide vane expands to the outer circumferencial direction by centrifugal force and the swirling state abruptly declines. Another is a newly developed type “Wing-curved swirler” in which the bending angle of the guide vane becomes deeper from the center to the outer direction. The air flow maintains the swirling force and the recirculation flow is wider than the former “Bent plate swirler”. The Wing-curved swirler with a high swirl force, a swirl number of 2 or more, not only increases the swirl of the sprayed droplet but also lengthens its trajectories. The flame stability was improved by the burner equipped with the developed Wing-curved swirler. The decrease in dust concentration was demonstrated through the residual oil combustion test of the 10 MW actual burner.