A piece type ball screw in a screw shaft with a spiral external thread groove on an outer peripheral surface, a nut which is fitted onto the screw shaft and has a spiral internal thread groove on an inner peripheral surface, a plurality of balls rotatably arranged in a track path formed between the external thread groove and the internal thread groove, and a piece member which is attached to the nut and connects the internal thread grooves to each other. The piece member includes a piece body in which a return groove connecting the internal thread grooves is formed and a pair of engaging portions which are provided on the piece body, extend in opposite directions in a circumferential direction of the nut, and engage with the internal thread groove of the nut. A joint portion between the piece body and the engaging portion has a fillet shape.