The present invention addresses the problem of providing an inspection method that is for determining an oral cavity index and that is capable of determining an oral cavity index. This inspection method for determining an oral cavity index includes: an image acquisition step for acquiring an ultrasonic image inside attached gingiva of a patient by using a measurement probe； an average brightness acquisition step for acquiring an average brightness of the ultrasonic image； and an index determination step for determining an oral cavity index of the patient by referring to a reference of the oral cavity index and the average brightness.本發明的課題在於提供一種可判定口腔內指數的判定口腔內指數的檢查方法，所述判定口腔內指數的檢查方法包括：圖像獲取步驟，利用測定探針，獲取受試者的附著牙齦內部的超音波圖像；平均亮度獲取步驟，獲取超音波圖像的平均亮度；以及指數判定步驟，參照平均亮度及口腔內指數的基準，判定受試者的口腔內指數。
