Chronic critical limb ischemia (CLI) is a progressive disease, which arises as a result of atherosclerosis or vasculitis in leg arteries. Prognosis of chronic CLI is poor, and no effective treatments have been established in patients who are not eligible for the traditional revascularization therapies such as angioplasty and bypass procedures due to the inappropriate anatomy of the leg arteries or frequent reocclusion following revascularization. Therefore, it is necessary to establish novel revascularization treatment to improve prognosis of the no-option patients. We will study the safety and clinical efficiency of vascular regeneration by means of transplantation of autologous peripheral blood endothelial progenitor cells (CD34 positive cells) in patients with chronic CLI who are not eligible for traditional revascularization treatments. The primary endpoint is the primary efficacy score identified by toe brachial blood pressure index (TBPI), absolute claudication distance (ACD) and Wong Baker's pain rating scale, while the secondary endpoints are evaluation of safety, ankle brachial blood pressure index (ABPI), percutaneous tissue oxygen pressure (TcPO2), etc.