A device controller, a peripheral device, and a power control method that enable buffers to be used efficiently and that enable power control to be performed on the basis of data amounts accumulated in the buffers are provided. A novel device controller includes an input buffer for accumulating data output from a host device, an output buffer for accumulating data output to the host device, a data communication section for transferring data between the input and output buffers and the host device, and a data buffer control section for modifying buffer allocation amounts to the input and output buffers on the basis of the data amount accumulated in at least one of the input and output buffers. The data buffer control section causes the data communication section to transition from a normal power consumption mode to a low power consumption mode when the data amount reaches a predetermined value.