An object of the present invention is to provide a mandrel having flexibility while maintaining heat resistance, releasability, and recyclability that can withstand a thermal history of repeated use, which are characteristics of 4-methyl-1-pentene-based polymer, and the present invention relates to a mandrel formed of a resin composition (X) including 50 to 90 parts by mass of a 4-methyl-1-pentene-based polymer (A) satisfying specified requirements, 5 to 40 parts by mass of a propylene polymer (B), and 5 to 30 parts by mass of a 4-methyl-1-pentene·α-olefin copolymer (C) satisfying specified requirements, provided that a total of the (A), the (B), and the (C) is 100 parts by mass.