The COVID-19 outbreak caused by the SARS-CoV-2 virus in late 2019 and early 2020 comprises a serious pandemic threat worldwide. Given the severity of the disease and the fact that there is no approved cure for this infectious disease, it seems reasonable to search for better candidates' drugs among approved antiviral or even antibacterial drugs for their anti-COVID-19 capability in contrast to the currently approved drugs. The enzyme main protease of SARS-CoV-2 that plays an important role in the virus life cycle seems to be a good target for inhibition by drugs. Accordingly, in the present work by using the molecular docking method we used the newly released coordinate structure of the protease as a target and 40 approved drugs from anti-viral, anti-parasite anti-malaria groups as ligands for docking experiments. Blind and active site-directed docking experiments were carried out on the optimized and equilibrated structure of protease at pH 7, 37 degrees centigrade of temperature, and 1 atmosphere of pressure. Our results indicate that based on binding energy, percent of binding site occupation, membrane transportability, and the maximum allowed dosage, erythromycin, clarithromycin, Amprenavir, Darunavir, Cefixime, and Tetracycline are among the enrolled drugs merit best parameters for clinical evaluation and their therapeutic potential in COVID-19 outbreak.