Provided are a medical device and a treatment method which allow easy formation of a hole using energy and easy expansion of the formed hole without loss of tissue and allow an increase in working efficiency.Provided is a medical device (10) for forming a hole in a tissue in a living body and expanding the hole, the medical device (10) including: a dilator (40) having a first lumen (45) formed inside and having a tip portion (42) in which the first lumen (45) opens on a distal side； and an output unit (21) that outputs energy for denaturing the tissue and forming a hole, in which the output unit (21) is disposed on a tip portion (32) and formed discontinuously in the circumferential direction of the tip portion (32), and the outer diameter of the tip portion (42) gradually decreases toward the distal side.
