The present invention provides a medical material and a blood purification apparatus each having high anti-thrombotic properties and high safety. The apparatus is produced by incorporating therein a medical material which has a hydrophilic copolymerization polymer present on a surface thereof which is to be in contact with blood, wherein particulate protuberances each having a particle diameter of 50 nm or more are present on the surface which is to be in contact with blood at a density of 3 particles/μm2 or less and the relaxation time of adsorbed water in the hydrophilic copolymerization polymer is 2.5×10−8 seconds or shorter and 5.0×10−10 seconds or longer at −40° C.
