To remove foreign objects mixed into pachinko balls, after the process of polishing the pachinko balls.

In this ball polishing device 13, balls collected from each pachinko machine in a pachinko machine installation island are received through an input port 13e and fed between an endless belt rotating mechanism 13a and a polishing cloth stretching mechanism 13b. After the balls are polished while being moved upward, they are passed through a ball guide gutter 13d provided at the rear end of the device 13 and are supplied to a ball lifting device 14. The ball guide gutter 13d is provided with an opening through which foreign objects mixed in the balls can fall, e.g. a slotted opening having slots d2 aligned along the direction of flow of the balls, as shown in Figure 1. A foreign object collecting box 13f that opens at its top is disposed immediately below the ball guide gutter 13d in such a manner as to be freely attachable to and removable from a vertical side plate 13y.