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.
