A treatment device is disclosed for treatment of a living body lumen. The treatment device can include an optical fiber having an emitting part that emits laser light from a side circumferential surface. Two or more grooves are provided in the emitting part at places different in a longitudinal direction of the emitting part. The two or more grooves have two or more kinds of shapes and intensities of the laser light emitted from the grooves adjacent to each other are different. A maximum region of intensity of the laser light emitted from the emitting part is located on one end side relative to a center position in the longitudinal direction of the emitting part. The intensity of the laser light emitted from the emitting part on the other end side of the emitting part relative to a position of the maximum region decreases toward the other end side.