To prevent complication caused by leakage of bone cement injected into the vertebral body, organism damage caused by the leakage of the monomer or a non-cured component from bone cement and decrease of strength caused by insufficient curing of bone cement, in the percutaneous kyphoplasty, a leakage prevention bag for injecting and filling a bone cement is used, wherein the bad is made of a bioabsorbable material having a molecular weight of 5,000 to 500,000 and has a bag having the thickness of 10 to 800 .mu.m, an injection tube is attached to an injection port for injecting the bone cement of the bag, the bag is inserted into a cavity formed in the vertebra body, and the bone cement is injected and filled into the bag through the tube.