An inflammatory pseudotumor is a rare benign disease presenting with non–specific chronic inflammation, and reported occurrences involving the skull base are relatively rare. A 65-year-old man became aware of pain around the right temporomandibular joint and mild trismus, and palsies of the cranial nerves III, IV, V, and VI were observed. A biopsy was performed under general anesthesia with an infratemporal fossa approach, and he was diagnosed with inflammatory pseudotumor of the infratemporal fossa. There was a rapid improvement in symptoms after the start of steroid administration, and 29 months after the initial consultation, the patient remained under strict observation. The 3 criteria in our department for confirming progression of the disease are (1) clinical symptoms, (2) C-reactive protein levels in blood tests, and (3) contrast effect of the tumor on magnetic resonance imaging. This is a rare case report to demonstrate the inflammatory pseudotumor of the infratemporal fossa leading to orbital apex syndrome.