For treatment of a patient who has a lesion in each of left lower limb artery and right lower limb artery, lesions at both sides can be rather easily and completely treated. A catheter is introduced from an artery of an arm of the patient, and an atherectomy catheter is used for a lesion at one side and continuously used for a lesion at the other side without being extracted to the outside of a human body, and thus damage of an excision portion of the atherectomy catheter and an unexpected situation such as no passage through twisted blood vessels are avoided so that a burden on the patient can be reduced, the treatment can be completed within a short time, and cost reduction can be achieved by reducing the number of catheter to be used.