A treatment method reduces the time required to exchange a long catheter which is introduced from an arm to treat the lower limb artery. The treatment method involves introducing a first catheter from an artery of one arm of the patient to dispose a distal portion of the first catheter at least in front of the lesion area in the lower limb artery； introducing a second catheter from an artery of the other arm of the patient； disposing a first treatment catheter in the lesion area through the first catheter； treating the lesion area with the first treatment catheter； and assisting the treatment with the second catheter and/or a second treatment catheter that is inserted into the second catheter.
