A method of collecting a specimen of the present invention is used in detecting upper digestive system disease. The method of collecting a specimen includes: a step of positioning sampling equipment in the duodenum of the subject into which duodenal juice is secreted, the sampling equipment being used to collect and store the duodenal juice a step of collecting duodenal juice naturally secreted in the duodenum using the sampling equipment and a step of stopping collection of the duodenal juice when collection quantity of the duodenal juice reaches a predetermined quantity which is 3.0 ml or less.
