A 48-year-old male presented to our hospital with pyrexia and general fatigue. The patient was diagnosed with influenza A virus infection, and then given laninamivir octanoate hydrate. Eleven days after onset, he noticed bilateral swollen submandibular glands. He visited our hospital again, and underwent blood examination and cervical computed tomography (CT). CT indicated that bilateral submandibular glands were swelling. We believe that this is the first report of bilateral submandibular sialadenitis following influenza A virus infection, and thus we presented this patient.