WE CLAIM:
1. A copolymer comprising a monomer unit A, a monomer unit B, and a monomer unit C that are represented by-general formula (I) shown below,
wherein a mole fraction of the monomer unit C based on all monomer units that constitute the copolymer is 0.5 to 40%: [Chemical Formula 1]
wherein RA represents a functional group having an amide bond, RB represents an alkyl or an alkenyl having 2 to 20 carbon atoms, Rc represents an alkyl or an alkenyl in which an arbitrary hydrogen atom is substituted with at least one functional group selected from the group consisting of an amino group, an azido group, an imino group, a carboxy group, an acid chloride group, an acid anhydride group, an aldehyde group, a hydroxyl group, a phosphoric acid group, a thiol group, an isocyanate group, a thioisocyanate group, an epoxy group, a halogenated alkyl

group, a cyano group, a vinyl group, an ethynyl group, a nitro group and a nitroso group, and ionized functional groups thereof (wherein an arbitrary carbon atom in the alkyl or the alkenyl of Rc is optionally substituted with a nitrogen atom, an oxygen atom, or a sulfur atom), and X1, X2, and X3 each represent a hydrogen atom or a methyl group.
2. The copolymer according to claim 1, wherein the monomer unit A is represented by any one of general formulae (II) to (IV) shown below: [Chemical Formula 2]

wherein m represents an integer of 1 to 5.
3. The copolymer according to claim 1 or 2, wherein the monomer unit A, the monomer unit B, and the monomer unit C are randomly arranged.
4. The copolymer according to any one of claims 1 to 3, having a number average molecular weight of 1,000 to 100,000.
5. The copolymer according to any one of claims 1 to 4, wherein Rc is an alkyl group in which an arbitrary hydrogen atom is substituted with at least one functional group selected from an amino group, an isocyanate group, and an epoxy group.
6. A medical material containing the copolymer according to any one of claims 1 to 5, and a base material bonded to the copolymer.

7. The medical material according to claim 6, wherein the base material is made from a polymer .having a repeating unit containing an ester bond in a main chain.
8. The medical material according to claim 6, further comprising a phosphonic acid derivative or a catechol derivative,
wherein the base material is made of a metal,
the copolymer is bonded to the phosphonic acid derivative or the catechol derivative,
the phosphonic acid derivative is bonded to the base material via a phosphonic acid group thereof, and
the catechol derivative is bonded to the base material via a catechol group thereof.
9. A thrombus capture device including the medical material according to any one of claims 6 to 8.
10. The medical material according to claim 6, wherein the base material is made from a polymer a part of which contains a hydroxyl group or a carboxy group introduced therein and in which at least, one hydrogen atom in a main chain is substituted with a chlorine atom, or a polymer a part of which contains a hydroxyl group or a carboxy group introduced therein and that has a siloxane bond in at least

a part thereof, and the copolymer is bonded to the base material via the hydroxyl group or the carboxy group.
11. A blood circuit including the medical material according to claim 10.