Anti-melanoma differentiation-associated protein 5 (anti-MDA5) antibody-positive dermatomyositis (DM) is a subtype of DM described recently. It has atypical features compared with classical DM, such as cutaneous ulcers, interstitial lung disease (ILD), arthritis, and less muscle involvement. We presented a patient diagnosed with anti-MDA5 antibody-positive DM with severe cutaneous ulcers, whose symptoms started after an electrical injury trauma. The patient was a 33-year-old man who was admitted to our department with skin rash, arthralgia, and weakness developing during the last 2 months. In his medical history, he sustained a low-voltage electrical injury 1 month ago. He was diagnosed with DM according to the physical examination, laboratory, and radiological findings and cutaneous histopathology. Treatment with oral administration of prednisolone 1 mg/kg/day and intravenous administration of immunoglobulin 2 g/kg/day was initiated. At the start of symptom improvement, the prednisolone dose was gradually tapered. At the third visit, his condition deteriorated, presenting with cutaneous and mucosal ulcers. At this point, the extended myositis panel was sent, and anti-MDA5 antibody was detected. High-resolution computed tomography revealed peripheral intralobular reticular opacities on both lungs, which indicated ILD in the early stage. Therefore, intravenous administration of cyclophosphamide 1000 mg once a month was added to steroid and intravenous immunoglobulin. His treatment continued with dramatic improvement. Anti-MDA5 antibody-positive DM has a significant risk of developing rapidly progressive ILD, therefore diagnosing timely is critical for prognosis.