A micelle preparation containing an anti-cancer agent, the preparation exhibiting sustained drug release capability, and enabling an extension of a retention time period of the anti-cancer agent in the abdominal cavity, comprising: a copolymer having a hydrophilic polymeric moiety and a polycarboxylic acid derivative moiety represented by the formula: where n is an integer of from 100 to 300, x or y is an integer of 1 or more, z is an integer of 1 or more, (x + y + z) is an integer of from 10 to 80, the ratio of x to (x + y + z) is 0 to 90%, the ratio of y to (x + y + z) is 0 to 90%, the ratio of z to (x + y + z) is 1 to 80%, and R is a combination of one or more selected from hydroxy, 4-phenyl-1-butoxy, and isopropylaminocarbonyl-isopropylamino groups, with the proviso that the ratio of the hydroxy group to (x + y + z) is 0 to 10%, the ratio of the 4-phenyl-1-butoxy group to (x + y + z) is 10 to 90%, and the ratio of the isopropylaminocarbonyl-isopropylamino group to (x + y + z) is 5 to 30%, and an anti-cancer agent bonding to or encapsulated in the copolymer; or a polymeric derivative drug derived from camptothecins, represented by formula: where t is an integer of from 100 to 300, (d + e + f) is an integer of from 6 to 60, the ratio of d to (d + e + f) is 0 to 60%, the ratio of e to (d + e + f) is 0 to 60%, the ratio of f to (d + e + f) is 1 to 100%, and R is an isopropylaminocarbonyl-isopropylamino group; for use in the prevention and treatment of peritoneal disseminated metastasis, or the treatment of cancers occurring in an organ present in the abdominal cavity, stomach cancer, colorectal cancer, pancreatic cancer, liver cancer, gall bladder cancer, ovarian cancer, uterine cancer, kidney cancer, ureteral cancer, or peritoneal cancer, by intraperitoneal administration. a copolymer having a hydrophilic polymeric moiety and a polycarboxylic acid derivative moiety represented by the formula: where n is an integer of from 100 to 300, x or y is an integer of 1 or more, z is an integer of 1 or more, (x + y + z) is an integer of from 10 to 80, the ratio of x to (x + y + z) is 0 to 90%, the ratio of y to (x + y + z) is 0 to 90%, the ratio of z to (x + y + z) is 1 to 80%, and R is a combination of one or more selected from hydroxy, 4-phenyl-1-butoxy, and isopropylaminocarbonyl-isopropylamino groups, with the proviso that the ratio of the hydroxy group to (x + y + z) is 0 to 10%, the ratio of the 4-phenyl-1-butoxy group to (x + y + z) is 10 to 90%, and the ratio of the isopropylaminocarbonyl-isopropylamino group to (x + y + z) is 5 to 30%, and an anti-cancer agent bonding to or encapsulated in the copolymer; or n is an integer of from 100 to 300, x or y is an integer of 1 or more, z is an integer of 1 or more, (x + y + z) is an integer of from 10 to 80, the ratio of x to (x + y + z) is 0 to 90%, the ratio of y to (x + y + z) is 0 to 90%, the ratio of z to (x + y + z) is 1 to 80%, and R is a combination of one or more selected from hydroxy, 4-phenyl-1-butoxy, and isopropylaminocarbonyl-isopropylamino groups, with the proviso that the ratio of the hydroxy group to (x + y + z) is 0 to 10%, the ratio of the 4-phenyl-1-butoxy group to (x + y + z) is 10 to 90%, and the ratio of the isopropylaminocarbonyl-isopropylamino group to (x + y + z) is 5 to 30%, and an anti-cancer agent bonding to or encapsulated in the copolymer; or a polymeric derivative drug derived from camptothecins, represented by formula: where t is an integer of from 100 to 300, (d + e + f) is an integer of from 6 to 60, the ratio of d to (d + e + f) is 0 to 60%, the ratio of e to (d + e + f) is 0 to 60%, the ratio of f to (d + e + f) is 1 to 100%, and R is an isopropylaminocarbonyl-isopropylamino group; for use in the prevention and treatment of peritoneal disseminated metastasis, or the treatment of cancers occurring in an organ present in the abdominal cavity, stomach cancer, colorectal cancer, pancreatic cancer, liver cancer, gall bladder cancer, ovarian cancer, uterine cancer, kidney cancer, ureteral cancer, or peritoneal cancer, by intraperitoneal administration. t is an integer of from 100 to 300, (d + e + f) is an integer of from 6 to 60, the ratio of d to (d + e + f) is 0 to 60%, the ratio of e to (d + e + f) is 0 to 60%, the ratio of f to (d + e + f) is 1 to 100%, and R is an isopropylaminocarbonyl-isopropylamino group; for use in the prevention and treatment of peritoneal disseminated metastasis, or the treatment of cancers occurring in an organ present in the abdominal cavity, stomach cancer, colorectal cancer, pancreatic cancer, liver cancer, gall bladder cancer, ovarian cancer, uterine cancer, kidney cancer, ureteral cancer, or peritoneal cancer, by intraperitoneal administration.