A disk storage medium processing apparatus includes an apparatus body having a disk loading/unloading slot, a traverse unit disposed in the apparatus body, a disk conveying device which conveys the disk into or from the apparatus body, and a control device for controlling the disk conveying device. The disk conveying device includes first through third disk conveying arms pivotably attached to the apparatus body to hold a periphery of the disk to convey. The control device includes a trigger setting device for setting trigger for starting control of the disk conveying device according to a diameter of the disk. The trigger setting device moves in a vertical direction according to an amount of pivotal movement of at least one of the first through third disk conveying arms, and sets the trigger.