To provide a ball screw device which equalizes passage diameters of turning passages by equalizing a distance between centers along the axial direction of a ball screw nut in the state of a fitting body being fitted in the ball screw nut, and also to provide a method for manufacturing the ball screw device.

The inner wheel 37a of a bearing 37 is fitted in a fitting portion W of the ball screw nut 33, in the ball screw device. In this state, the depth D of a screw groove 34a is adjusted so that the distance M between the centers from the central shaft L2 (shaft center) of the ball screw nut 33 to the center P of ball 32 arranged in the screw groove 34a of the ball screw nut 33, is equalized along the axial direction of the ball screw nut 33. That is, the depth D1 of the screw groove 34a positioned in the inner periphery of the fitting portion W before the inner wheel 37a is fitted in, is formed deeper than that of the screw groove 34a positioned in the inner periphery of other portions.