Urban ore is a mixture of a lot of metallic elements, and these metallic elements need to be separately collected therefrom. However, because the content of each metallic element is very small, it has been extremely difficult to selectively collect the required metallic element.In order to solve the problem, there is provided a metal-ion adsorbent which is for use in a method for collecting metal ions present in a liquid, and in which a continuously porous support having large numbers of pores of uniform size and shape, and a compound having a metal ion-binding group is chemically bonded to the inner surfaces of the pores, whereby a material and a method with which rare-metal ions contained in urban ore are efficiently and inexpensively taken out are provided.