To ensure the safety of painted steel structures, it is important to evaluate the influence of the size and proximity of coating defects on corrosion behavior. In this research, accelerated exposure tests were carried out using combined corrosion cycles, which consisted of exposure to atomizing salt water, wetting, and drying with hot and warm wind. The test specimens were paint-coated steel plates with individual circular machined coating defects 1, 3, 10, and 15 mm in diameter. Multi-circular defects 1 mm in diameter were also created in the specimens. The test results indicate that the mean and maximum corrosion depths increased with increasing diameter of the single defect of the coated steel plate. When actual coated steel members are exposed to corrosive chloride environments such as those represented by the corrosion cycle testing conducted in this research, the corrosion depth for multi-circular defects 1 mm in diameter appears to be 1.5 to 2.5 times greater than that for a single-circular defect.