The present invention provides a substrate for ligand immobilization, which comprises a water-insoluble carrier and a copolymer represented by general formula (1) bound to at least the surface of the water-insoluble carrier. [In general formula (1), n and m represent positive integers and the value of m/(n+m) is 0.05 to 0.50. Moreover, in general formula (1), R1 is H or CH3, R2 is an organic group having electrophilic functional groups, and R3 is a group represented by general formula (2). In general formula (2), Y is O or NH, p is 1 or 2, and q is 2 or 3.]