The present invention addresses the problem of providing an agent for inducing regulatory dendritic cells that can be applied to treating immune diseases, is safe, and has a different mechanism of action than existing drugs, and also providing an immune tolerance inducer such as an agent for preventing/treating allergic disease or an agent for preventing/treating autoimmune disease. The problem is solved by preparing an immune tolerance inducer in which the active ingredients are 5-aminolevulinic acid (ALA), or a derivative or salt thereof, and an iron compound. The ALA can be preferably exemplified by ALA or a variety of esters thereof, such as the methyl, ethyl, propyl, butyl, or pentyl ester, as well as the hydrochlorides, phosphates, sulfates, or the like thereof, and the iron compound can be preferably exemplified by sodium ferrous citrate.本發明課題為提供一種免疫耐受誘導劑，其係安全且與先前藥劑作用機構不同之可應用於免疫疾病之治療的控制性樹狀細胞之誘導劑，除此之外的過敏性疾病之預防治療劑或自體免疫疾病之預防治療劑等。本發明之解決方法，係調製免疫耐受誘導劑，其將5-胺乙醯丙酸(ALA)或者其衍生物或其鹽、及鐵化合物作為有效成分。以上述ALA類而言，可適當例示ALA、及同甲酯、乙酯、丙酯、丁酯、戊酯等之各種酯類、以及該等鹽酸鹽、磷酸鹽、硫酸鹽等，以鐵化合物而言，可適當例示檸檬酸亞鐵鈉。
