The present invention addresses the problem of obtaining an anti-repulsive guidance molecule a (RGMa) antibody which has a high binding activity and few side effects and can be used as a medicine for preventing, treating, or preventing the relapse of neurological or immunological diseases. Said problem is solved by providing an isolated RGMa binding protein which does not inhibit binding between RGMa and neogenin, but neutralizes the neuritis growth inhibiting activity of RGMa, and preferably by providing an anti-RGMa antibody which has a complementarity determining region having an amino acid sequence of SEQ ID NOS: 30-35 or SEQ ID NOS: 36-40 in the sequence listing, and SFG.本發明之課題為得到可使用作為神經學疾病或免疫學疾病之預防、治療或復發預防用之醫藥的結合活性高、且副作用少之抗Repulsive Guidance Molecule a(RGMa)抗體，藉由提供不阻礙RGMa與Neogenin之結合，且中和RGMa之神經突成長阻礙活性的經單離之RGMa結合蛋白質，較佳為，互補性決定區域之胺基酸序列為序列表之序列編號30~35或序列表之序列編號36~40及SFG的抗RGMa抗體，而解決其課題。
