According to one embodiment, a disk storage apparatus includes a read controller and a servo controller. The read controller contains a combined position generator including a state observer and a combined position calculator. The servo controller controls a seek operation of the head based on the combined position. The servo controller stores the servo information in a memory and determines an occurrence of a state offset as an error between an actual position of the head and the combined position. The servo controller corrects the predicted position by the state observer based on the servo information stored in the memory and the combined position when the occurrence of the state offset is detected.