PROBLEM TO BE SOLVED: To provide a polyvinyl acetal porous body suitable for use of a medical application.MEANS FOR SOLVING THE PROBLEM: A polyvinyl acetal resin porous body 2 and a formaldehyde adsorption 3 are irradiated with an electron beam or a gamma ray from the outside of a packaging bag 4 in a state where the polyvinyl acetal resin porous body 2 and the formaldehyde adsorption 3 are accommodated and sealed in the packaging bag 4.SELECTED DRAWING: Figure 1