Medical device and treatment method

A medical device for cutting substances inside a body lumen, the medical device comprising:

• a drive shaft that is rotatable;
• a cutting unit configured to be rotatably connected to a distal side of the drive shaft;
• a linear motion shaft configured to adjust a deformation amount of the cutting unit;
• a filter device configured to be inserted in a contracted state into the body lumen, the filter device having an elongated shaft, which interlocks with a filter portion of the filter device;
• a distal tube, the distal tube being on a distal side of the cutting unit, and wherein the distal tube is configured to receive the elongated shaft of the filter device;
• a housing containing a motor;
• and
• a first drive gear connected to the drive shaft, a second drive gear connected to the motor via a rotary shaft and meshing with the first drive gear, a first partition wall arranged between the motor and the second drive gear, a second partition wall arranged proximal to the first partition wall, and wherein the rotary shaft fixed to the motor extends through the first partition wall to the second drive gear, and the first drive gear and the second drive gear are between the first partition wall and the second partition wall.