We evaluated GeneFinder COVID-19 Ag Plus Rapid Test for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and its performance was compared to the real-time reverse transcription-polymerase chain reaction (RT-PCR) test. Samples were obtained once from 310 suspected patients of coronavirus diseases 2019 (COVID-19) and transported in universal transport medium (UTM). The samples were tested with STANDARD M nCoV Real-Time Detection kit or Allplex 2019-nCoV Assay which are real-time RT-PCR tests approved by Emergency-Use-Authorization in South Korea. Clinical information including symptom onset and test results including cycle threshold (Ct) values were obtained at the day of RT-PCR test. The remaining stored samples were tested with GeneFinder COVID-19 Ag Plus Rapid Test. Out of 310 patients recruited, RT-PCR was positive in 140 patients and GeneFinder COVID-19 Ag Plus Rapid Test was positive in 118 patients. The overall sensitivity and specificity of GeneFinder COVID-19 Ag Plus Rapid Test in detection of SARS-CoV-2 compared to RT-PCR tests were 84.3% (95% confidence interval [CI], 77.0% - 89.7%) and 100% (95% CI, 97.2% - 100.0%), respectively. In patients with Ct values under 20, the sensitivity was 100% (95% CI, 92.8% - 100.0%). The sensitivity was 94.2% (95% CI, 83.1% - 98.5%) in patients with Ct values from 20 to 25 and 54.5% (95% CI, 24.6% - 81.9%) in patients with Ct values from 25 to 30. Patients with positive RT-PCR were classified into three groups according to symptom onset for further analysis. The sensitivity was 92.7% (95% CI, 79.0% - 98.1%) in patients whose symptoms appeared less than 3 days prior to RT-PCR. The sensitivity decreased to 71.1% (95% CI, 55.5% - 83.2%) in patients whose symptoms appeared more than 6 days prior to RT-PCR. The results indicate that the GeneFinder COVID-19 Ag Plus Rapid Test may be a convenient tool in quickly identifying and preventing COVID-19 transmission.