The present invention provides a disk device, a control device, and a positioning control method with which positioning in a target position can be performed without expending time on a seek operation even when virtual circular control is performed using an eccentric disk. Virtual circular orbits, each depicting a perfect circle centered on the rotary center of a disk surface, are determined. An average orbit is then determined by averaging the virtual circular orbits. Orbits obtained by subtracting the average orbit from each virtual circular orbit are set as the position orbits of the respective disk surfaces. An MCU controls an actuator to follow these orbits.