Clinical Efficacy of Nafamostat Mesylate for COVID-19 Pneumonia

* Inclusion Criteria: 1. 18 years old or older 2. Patients who have been confirmed of COVID-19 infection and has evidence for pneumonia * Confirmation of COVID-19 infection by RT-PCR of SARS-CoV-2 * Definite diagnosis of new infiltration of the lungs by chest CT scan of chest radiographic inspection 3. Patients who are within 72 hours of COVID-19 pneumonia confirmation 4. Patients with 3(hospitalization, not requiring supplemental oxygen) or higher in seven-category ordinal scale of clinical status * Seven-category ordinal scale of clinical status 1. not hospitalized with resumption of normal activities; 2. not hospitalized, but unable to resume normal activities; 3. hospitalization, not requiring supplemental oxygen; 4. hospitalization, requiring supplemental oxygen; 5. hospitalization, requiring nasal high-flow oxygen therapy and/or noninvasive mechanical ventilation; 6. hospitalization, requiring extracorporeal membrane oxygenation and/or invasive mechanical ventilation; 7. death. 5. Patients who are eligible for diagnosis/evaluation to chest CT scan and related to it 6. Patients should be able to understand the essence of the clinical trial and to submit a written consent document. For the patients who can understand the nature of the research but cannot sign the document, a relative can agree to the study. * Exclusion Criteria: 1. Patients who have a record of HIV or AIDS 2. Female patients, either who are pregnant within 6 months before the investigation, who breast-fed babies within 3 months before the investigation, or who may get pregnant or breast-feed within 1 month after the investigation is over 3. Patients at high risk of death within 3 days of randomized assignment, by the judge of the investigator 4. Patients with liver cirrhosis whose Child-Puch score is B or C 5. Patients who have liver disease abnormalities with ALT or AST \> 5 times ULN 6. Patients who can be in danger or who shows clinically-important other conditions which may interfere with the evaluation or completion of the test procedure, as the investigator's opinion 7. Patients who are not appropriate for the test, as the investigator's opinion 8. Patients who have hypersensitivity to the investigational drug