Abstract: A driving shaft (3) includes an inner tube (1) and an outer tube (2) having a modified cross-section. These tubes (1, 2) are axially movable but not rotatable relative to each other for transmitting torque therebetween. The driving shaft (3) comprises a partition unit having a pair of partition walls (8a, 8b; 16) hermetically sealing at least part of the inside of the inner tube to define a grease reserving space (8A) in the inner tube on the side of its distal end. The partition wall (8a, 16) on the side of its proximal end is provided with a hose mounting portion (8c; 23) having an oil hole (9). The driving shaft (3) further comprises an oiling port unit (10; 20) provided on a fitting yoke (7) on the side of the proximal end of the inner tube and an oiling conduit unit (11; 24, 25) for connecting the oiling port unit (10; 20) and the hose mounting portion (8c; 23) of the partition unit.