An antitumor drug delivery formulation for use in treating a subject having a tumor more highly expressing a TUG1 gene than normal tissues or preventing tumor metastasis in the subject, comprising a polymeric micelle comprising a nucleic acid that suppresses expression of the TUG1 gene as an active ingredient; wherein the polymeric micelle comprises a block copolymer having a cationic poly(amino acid) segment and a hydrophilic polymer chain segment and the nucleic acid, wherein the nucleic acid is bound to a cationic group of the cationic poly(amino acid) segment to form a complex and/or the nucleic acid is incorporated in the micelle or attached into the micelle; wherein the nucleic acid is selected from the group consisting of: (a) any one or a combination of two or more of siRNAs, precursor RNAs thereof, or modified RNAs thereof, each comprising a sense strand consisting of the nucleotide sequence of any of SEQ ID NOs: 7 to 11 and an antisense strand consisting of the nucleotide sequence of any of SEQ ID NOs: 15 to 19 complementary to the sense strand; and (b) (i) an antisense RNA comprising at each end at least two LNA modified nucleotides and having the nucleotide sequence of any of SEQ ID NOs: 28 to 35; or (ii) an antisense DNA comprising at each end at least two LNA modified nucleotides and having nucleotide sequences of any of SEQ ID NOs: 28 to 35 which have been modified by substituting uracil with thymine; and wherein the polymeric micelle accumulates in the tumor, wherein the tumor is brain tumor, pancreatic cancer, breast cancer, colorectal cancer, prostate cancer, liver cancer, lung cancer, leukemia, or lymphoma. wherein the polymeric micelle comprises a block copolymer having a cationic poly(amino acid) segment and a hydrophilic polymer chain segment and the nucleic acid, wherein the nucleic acid is bound to a cationic group of the cationic poly(amino acid) segment to form a complex and/or the nucleic acid is incorporated in the micelle or attached into the micelle; wherein the nucleic acid is selected from the group consisting of: (a) any one or a combination of two or more of siRNAs, precursor RNAs thereof, or modified RNAs thereof, each comprising a sense strand consisting of the nucleotide sequence of any of SEQ ID NOs: 7 to 11 and an antisense strand consisting of the nucleotide sequence of any of SEQ ID NOs: 15 to 19 complementary to the sense strand; and (b) (i) an antisense RNA comprising at each end at least two LNA modified nucleotides and having the nucleotide sequence of any of SEQ ID NOs: 28 to 35; or (ii) an antisense DNA comprising at each end at least two LNA modified nucleotides and having nucleotide sequences of any of SEQ ID NOs: 28 to 35 which have been modified by substituting uracil with thymine; (a) any one or a combination of two or more of siRNAs, precursor RNAs thereof, or modified RNAs thereof, each comprising a sense strand consisting of the nucleotide sequence of any of SEQ ID NOs: 7 to 11 and an antisense strand consisting of the nucleotide sequence of any of SEQ ID NOs: 15 to 19 complementary to the sense strand; and (b) (i) an antisense RNA comprising at each end at least two LNA modified nucleotides and having the nucleotide sequence of any of SEQ ID NOs: 28 to 35; or (ii) an antisense DNA comprising at each end at least two LNA modified nucleotides and having nucleotide sequences of any of SEQ ID NOs: 28 to 35 which have been modified by substituting uracil with thymine; and wherein the polymeric micelle accumulates in the tumor, wherein the tumor is brain tumor, pancreatic cancer, breast cancer, colorectal cancer, prostate cancer, liver cancer, lung cancer, leukemia, or lymphoma.