The problems: It is an object of the present invention to provide an immune regulating agent capable of modulating a receptor function concerning immune regulation of DR6, and a method for screening thereof.The object aims to provide: The present invention relates to an immune regulating agent containing a physiologically active substance having an ability to bind specifically to DR6 and an ability to regulate signal transduction induced by specific binding between DR6 and Sdc1, as an active component. The immune regulating agent of the present invention can be used for treating or preventing diseases caused by excessive or abnormal immune response in mammals or diseases for which enhancement of immune function is desired in mammals, as an immune regulating agent based on a hitherto unknown mechanism, capable of regulating signal transduction induced by specific binding between DR6 and Sdc1.