A power source control apparatus for a disk subsystem includes a plurality of hard disk drives (HDDs) each with two systems of fiber channel interface ports, an HDD drive section, and an HDD control logic section. The HDD drive section includes two systems of fiber channel control sections, each of which includes a fiber channel interface and a fiber channel control interface. The HDD control logic section includes two systems of HDD control logics that control read/write accesses to the HDDs. Fiber channel control signals are supplied from the HDD control logics to the fiber channel control interfaces, respectively, and the fiber channel control signals are also used to control the power source of the HDD drive section.