A tube main body (12) of a curved tube (10) has a flow path following an axis line (12A), and includes a bent portion (14) at one portion in a direction along the axis line (12A). Also, in an inner periphery (14A) inside a bending direction of the bent portion (14) in the tube main body (12), a concave portion (16) is formed as an enlarged cross-section portion along a direction of the axis line (12A). Incidentally, in an inner die of a die for forming a curved tube, a hinge core forming the concave portion (16) is inserted in a groove portion of a main core, and the main core moves in a retraction-positional direction, so that a tip portion of the hinge core having a shape engaging with the inner periphery (14A) inside the bending direction of the bent portion (14) swings to a formation position of the main core.