To provide a driving shaft capable of preventing rattling caused by abrasion and seizure, by keeping good sliding of contact faces and smooth rolling of a ball on a raceway face for a long period in out of grease in comparison with a case when the driving shaft is coated with a resin coating film.

This driving shaft 1 is constituted by coating a power transmission face 21 of at least one of a male spline shaft 2 and a female spline shaft 3 to the other, with a coating film 6 having Vickers hardness Hv of 1000 or more, and a coefficient of friction μ of 0.25 or less.