To provide a polymer improved in stability and safety which had trouble in a conventional technique and capable of simultaneously realizing preferable characteristics such as good mechanical properties, ready processability, ready control of hardness, properties capable of readily imparting functionality by selection of a raw material and good biocompatibility.

This phosphorus-containing polymer containing phosphorus introduced by urethane bond and/or urea bond and covalent bond and/or ionic bond in the molecule. In the polymer, the phosphorus concentration in an extracted solution obtained by carrying out extraction operation of the polymer with physiological saline at 50°C for 72 hr at a bath ratio of 20 ml physiological saline to 4.0 g polymer is ≤300 ppm. The phosphorus-containing polymer is preferably a polymer containing urethane bond and/or urea bond and a phosphate bond, obtained by combinedly using an aliphatic diisocyanate and an aromatic diisocyanate as a diisocyanate component in the molecule, more preferably a phosphorus-containing polymer having a structure represented by the chemical formula (2) or the chemical formula (3).