Hemangiomas are benign vascular soft tissue tumors, which most frequently occur in the skin or subcutaneous tissue. Intramuscular hemangiomas typically occur in the trunk and extremities and less frequently in the head and neck. Among these, those occurring in the temporalis muscle are extremely rare. The authors report the case of a 43-year-old Japanese male with a mass in his left temporal fossa. Computed tomography images showed no erosion of the zygomatic bone, and magnetic resonance imaging revealed an ovoid well-marginated mass within the temporal muscle. The lesion was surgically excised with an endoscopy procedure used for minimally invasive lesions and complete removal. Histopathological examination confirmed the diagnosis of intramuscular cavernous hemangioma. The postoperative clinical course was good, with no indications of temporary nerve paralysis. No signs of local recurrence were observed postoperatively. Therefore, a cavernous hemangioma should be suspected when a mass occurs in the temporal region with accompanying radiologic findings suggesting vascular origin. In surgical treatment, the endoscopy-assisted technique is very useful to achieve complete tumor resection and prevent relapse while avoiding serious complications due to surgical procedures.