Abstract: A magnetic disk drive apparatus includes a velocity/position estimator of a magnetic head, in which a gain can automatically be adjusted in accordance with a moving velocity of the magnetic head. The velocity/position estimator generates a current head velocity estimated value and a current head position estimated value from a current head position predicted value, a current head velocity predicted value, a current estimated error value, a current head position estimated gain value and a current head velocity estimated gain value, wherein the current head velocity estimated value and the current head position estimated value, respectively, are determined in accordance with the current estimated error value and outputs of a subtracting unit which are respectively calculated by subtracting a velocity command value set according to a position error from the current head position estimated gain value and by subtracting the velocity command value from the current head velocity estimated gain value.