Provided is a treatment method that reduces risk factors contributing to anastomotic leakage by using a medical device. The treatment method includes placing a medical device including a sheet-like main body portion for promoting adhesion between biological tissues between one joint target site and another joint target site of a biological organ to be joined, and joining the one joint target site and the other joint target site to each other in a state where at least a portion of the main body portion is interposed between the one joint target site and the other joint target site.
