To provide a piece (deflector) type ball screw capable of simplifying assembling work of deflector members, and preventing generation of abnormal noise and vibration by permitting smooth rolling of balls.

In this piece (deflector) type ball screw comprising the deflector members 7 fitted to deflector windows 6 formed on a barrel part of a nut 3 and having connection grooves 8 applying a rolling path as a revolving path, arms 9 are projected from the deflector members 7 in a state of being engaged with a thread groove 4 of the nut 3 through a prescribed radial clearance, the deflector members 7 are fitted to the deflector windows 6 with play, elastic members 12 are mounted on annular grooves 10 formed on outer peripheral faces of the deflector members 7, and the deflector members 7 are elastically supported to bearing surfaces 11 formed on the deflector windows 6 of the nut 3 through the elastic members 12. Thus the deflector members 7 are elastically displaced in the radial direction even when the connection grooves 8 are projected from the thread groove 4 to be negative clearance, the balls 5 can be smoothly rolled, and error in working of each part can be absorbed by elastic deformation of the elastic members 12 mounted on the deflector members 7.