A magnetic disk device having a head IC on a magnetic head supporting mechanism. In order to secure the reliability by controlling the IC temperature below a predetermined level, the difference in the IC cooling ability varying with the radial position on the disk is quantified, so that power (signal) sufficient to maintain a constant temperature according to the IC temperature is supplied to the IC. Since the cooling ability at a given radial position of the IC is not exceeded by the power consumption, the IC temperature can be maintained below a predetermined level.