A 32-year-old man visited the emergency department complaining of the right scrotal pain, which occurred suddenly during sexual intercourse. Palpation revealed induration and tenderness on the caudal side of the right testis. Ultrasonography revealed a mosaic-like mass on the caudal side of the testis and no difference in blood flow between the right and left testes. The patient underwent a thorough examination the next day. Although the blood test did not show elevated tumor marker levels, testicular MRI revealed a mass with heterogeneous signal in the right scrotum. Subsequently, the patient was referred to another hospital for surgery. The pathological examination revealed a mixed germ cell tumor: seminoma (60%), teratoma (20%), and embryonal carcinoma (20%). One year postoperatively, the patient has had no recurrence. Testicular tumors are rarely discovered in acute scrotum, and few such cases have been reported. Torsion of the tumor, hemorrhage, necrosis, rupture, and infection have been reported as mechanisms of occurrence. When acute scrotum is diagnosed, testicular tumor should be considered as a differential diagnosis.