We investigated gas residence time and mixing characteristics due to various swirl numbers generated by normal injection of secondary air to a lab-scale cylinderical combustor. The residence time was estimated by measuring the temporal pressure difference which was caused by deposition of test particles on a filter media after the injection by a syringe. The mixing characteristics were evaluated by standard deviation value of test gas concentration at different measuring points. The test gas concentration was detected by a gas analyzer. The swirl number of $20{sim}30$ for ${ heta}=5^{circ}$ caused long residence time enough to improve mixing characteristics. Numerical calculations were also carried out to understand physical meanings of the experimental results.