To provide a non-bolt joint structure without the need for molding a dedicated polyethylene tube.

The non-bolt joint structure of a fluid tube comprises a seal ring 3 for sealing a gap between a receiving opening 1a and an insertion opening 2a, an engaging means 11 provided in the inner periphery of the receiving opening 1a, and engaged with the outer peripheral surface 25 of the polyethylene tube 2, for preventing the polyethylene tube 2 from breaking away from the receiving opening 1a, and a tubular metallic inner core 4 fitted into the inner periphery 26 of the insertion opening 2a of the polyethylene tube 2. An inner core 4 has a first expansion portion 40 which is plastically deformed to be curved in a longitudinal sectional shape to expand radially outward. A second expansion portion 20 is so deformed that the insertion opening 2a of the polyethylene tube 2 is expanded radially outward along the first expansion portion 40 of the inner core 4, and the engaging means 11 is engaged with the outer peripheral surface 25 of the second expansion portion 20, so that the polyethylene tube 2 can be prevented from breaking away.