Mycobacterium triviale is a subspecies of the Mycobacterium terrae complex, which rarely causes disease in humans. We encountered a case of respiratory infection, possibly caused by M. triviale, which was successfully treated by levofloxacin and clarithromycin. Although DNA-DNA hybridization identified M. triviale in one of three samples, clinical validations convinced us that it was the pathogen. 16s ribosomal RNA sequencing would have been reliable and ideal to perform in this case, although it is not covered by the insurance system in Japan. Nevertheless, this experience remains to be instructive because the clinical course, guidelines on the diagnosis, and therapeutic strategies for respiratory infections caused by M. triviale are not well-known or have not been established. Awareness of the possibility of respiratory infections caused by M. triviale and further collection and analysis of its predisposing conditions are essential.