An access control apparatus of a data storage device includes a first connecting unit configured to be removably connected with a power supply device, perform data transmission through a first data-transmission line, and be supplied with power through a first power-transmission line, a second connecting unit configured to be removably connected with the data storage device, perform data transmission through a second data-transmission line, and supply power through a second power-transmission line, a data transfer processing unit configured to perform data transfer between the power supply device and the data storage device, a power consumption measuring unit configured to measure power supplied from the power supply device through the first power-transmission line, and a power-transmission capability monitoring unit configured to control the data transfer processing unit in accordance with power consumption measured by the power consumption measuring unit.