Novel gadolinium complex compounds responsive to ions and compounds other than zinc ion and as well as MRI probes made of the compounds are disclosed. Since the gadolinium complex compounds of the present invention such as that represented by the following structural formula exhibit responsiveness to potassium ion, calcium ion, glucose or the like, by using the gadolinium complex compounds of the present invention as a MRI probe and the ion or compound in a living body can be detected and concentration distribution thereof may be determined.