A treatment unit includes: a communication part that receives through a communication cable information about a root canal length acquired by a root canal length measuring unit as an external diagnostic unit a display device on which the information about a root canal length is displayed and a treatment unit body to which a file for root canal enlargement is attached. The treatment unit body forms a holding part held by a user. The display device is provided on the outer circumference of the holding part. The user can visually recognize a root canal length displayed on the display device while performing root canal enlargement with the treatment unit held by the user.
