Provided are a halogen-free flame-retardant resin composition containing a metal hydroxide as a flame retardant, the resin composition having good flame retardancy even when a mixing proportion of the metal hydroxide is reduced and having good print quality, a flame-retardant heat-shrinkable tube formed by using the flame-retardant resin composition, and a flame-retardant insulated electric wire including an insulating coating formed by using the flame-retardant resin composition. The flame-retardant resin composition contains a thermoplastic resin, a metal hydroxide, and a modified silicone having, at an end thereof, a functional group having a carbon-carbon double bond. A content of the metal hydroxide is 85 to 190 parts by mass relative to 100 parts by mass of the thermoplastic resin, and a content of the modified silicone is 0.05% to 5% by mass relative to the metal hydroxide. The flame-retardant heat-shrinkable tube is formed by using the flame-retardant resin composition. The flame-retardant insulated electric wire includes an insulating coating formed by using the flame-retardant resin composition.
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