Inner fluted tube with excellent extrudability

Provided is an optimum fin shape with excellent extrudability and heat exchange efficiency compared to a conventional inner straight fluted tube that uses an aluminum alloy. Specifically provided is an inner fluted tube (100) made of an aluminum alloy, said tube having a plurality of pointed fins (102) that are present on an inner surface of the tube parallel to the longitudinal direction of the tube; the shape and position of said plurality of fins (102) on a cross section orthogonal to the longitudinal direction of said inner fluted tube (100) are roughly uniformly arranged in the circumferential direction of said inner fluted tube (100); and the ratio between the length (F(mm)) of the inner peripheral edge in said cross section and the area (A(mm )) of the fluted space section enclosed by circles that touch the inner peripheral edge and the tips of said plurality of fins (102) in said cross section is within a range of 10