A disk apparatus includes a disk driving section having a turntable, a transport mechanism for transporting a disk toward the disk driving section, detection members which abut against the edge of the disk to be transported and move in a direction crossing the disk transport direction in accordance with the peripheral shape of the disk, and a biasing member for biasing the detection members in a direction to be pressed into contact with the edge of the disk and urging the center of the transported disk to coincide with a transport center line passing through the center of the turntable. The disk apparatus also includes a position sensor for detecting the positions of the detection members, and a control section for stopping the disk transported by the transport mechanism when the movement of the disk to a predetermined position over the turntable is detected from an output of the position sensor corresponding to the positions of the detection members. Thus, the detection members move with the movement of the disk and the detection output from the position sensor continuously changes following the movement of the detection members, so that the control section stops the disk transported by the transport mechanism when the output from the position sensor reaches a peak value, whereby the disk is located at a predetermined position over the turntable. In addition, the control section discriminates the diameters of inserted disks on the basis of the amount of movement detected from the output of the position sensor. Therefore, the disk apparatus can certainly locate the disks with a small number of components, and discriminate the diameters of the disks.