To provide a flange for a paper tube improved in fitting force of the flange to be attached to the end of the paper tube.

A flange 30 for a paper tube detachably attached to the end of a pipe-shaped paper tube 21 is composed of a disc 1 having a concentric hole 2 on the central part, and a hollow cylindrical inserting member 3 extending from the hole 2 of the disc 1 along the central axis. A protrusion 31 to be engaged with the inner surface of the paper tube is provided on the outer periphery of the hollow cylindrical inserting member 3, and the sectional shape in the direction along the central axis of the protrusion 31 has pointed parts provided at both ends of the section and a recessed part provided between them.