A liquid retainer, comprising: a pouch (11; 41; 71) having water blocking properties and flexibility and formed into a pouch shape; and a three-dimensional knit: wherein the pouch (11; 41; 71) is formed into the pouch shape by welding outer edges of two films (14; 43, 44; 84) each made of one of resin and rubber to each other, wherein the pouch (11; 41; 71) comprises: an inlet side region (15; 45) continuous with an inlet port (11a; 41a) through which the liquid flows into the pouch (11; 41; 71); an outlet side region (16; 46) continuous with an outlet port (11b; 41b) through which the liquid flows out from the pouch (11; 41; 71); and a connection region (17; 47) connecting the inlet side region (15; 45) and the outlet side region (16; 46) to each other, wherein the pouch (11; 41; 71) comprises a welded portion (14b; 44b) formed by welding the two films (14; 43, 44; 84) to each other, the welded portion (14b; 44b) partitioning the inlet side region (15; 45), the outlet side region (16; 46), and the connection region (17; 47) from one another, wherein the three-dimensional knit is formed into a substantially flat-plate-like shape and arranged in substantially all of the inlet side region (15; 45), the outlet side region (16; 46), and the connection region (17; 47) in the pouch (11; 41; 71), wherein the liquid retained by the three-dimensional knit in the pouch (11; 41; 71) comprises one of cooling liquid and heating liquid, and wherein the liquid passes through the inlet side region (15; 45), the outlet side region (16; 46), and the connection region (17; 47) in the pouch (11; 41; 71) where the three-dimensional knit is arranged characterized in that the three-dimensional knit comprises: a plurality ofmesh-like knit garments arranged substantially parallel to eachother; and a plurality ofcoupling strands for coupling the plurality of mesh-like knit garments to each other, wherein the plurality of coupling strands are made of elastic chemical fiber. a pouch (11; 41; 71) having water blocking properties and flexibility and formed into a pouch shape; and a three-dimensional knit: wherein the pouch (11; 41; 71) is formed into the pouch shape by welding outer edges of two films (14; 43, 44; 84) each made of one of resin and rubber to each other, wherein the pouch (11; 41; 71) comprises: an inlet side region (15; 45) continuous with an inlet port (11a; 41a) through which the liquid flows into the pouch (11; 41; 71); an outlet side region (16; 46) continuous with an outlet port (11b; 41b) through which the liquid flows out from the pouch (11; 41; 71); and a connection region (17; 47) connecting the inlet side region (15; 45) and the outlet side region (16; 46) to each other, an inlet side region (15; 45) continuous with an inlet port (11a; 41a) through which the liquid flows into the pouch (11; 41; 71); an outlet side region (16; 46) continuous with an outlet port (11b; 41b) through which the liquid flows out from the pouch (11; 41; 71); and a connection region (17; 47) connecting the inlet side region (15; 45) and the outlet side region (16; 46) to each other, wherein the pouch (11; 41; 71) comprises a welded portion (14b; 44b) formed by welding the two films (14; 43, 44; 84) to each other, the welded portion (14b; 44b) partitioning the inlet side region (15; 45), the outlet side region (16; 46), and the connection region (17; 47) from one another, wherein the three-dimensional knit is formed into a substantially flat-plate-like shape and arranged in substantially all of the inlet side region (15; 45), the outlet side region (16; 46), and the connection region (17; 47) in the pouch (11; 41; 71), wherein the liquid retained by the three-dimensional knit in the pouch (11; 41; 71) comprises one of cooling liquid and heating liquid, and wherein the liquid passes through the inlet side region (15; 45), the outlet side region (16; 46), and the connection region (17; 47) in the pouch (11; 41; 71) where the three-dimensional knit is arranged characterized in that the three-dimensional knit comprises: a plurality ofmesh-like knit garments arranged substantially parallel to eachother; and a plurality ofcoupling strands for coupling the plurality of mesh-like knit garments to each other, a plurality ofmesh-like knit garments arranged substantially parallel to eachother; and a plurality ofcoupling strands for coupling the plurality of mesh-like knit garments to each other, wherein the plurality of coupling strands are made of elastic chemical fiber.