According to one embodiment, a storage device includes a processor which executes first processing, second processing and third processing. The second processing includes processing for relaying a command issued by a host device, and an execution result of the first processing corresponding to the. command, between the host device and the first processing. The third processing includes processing for causing the second processing to transition from a first state to a second state of lower energy consumption than the first state, when a first period in which the second processing is in an idle state exceeds a second period. The third processing further includes processing for maintaining the first state under a first condition, when the first period exceeds the second period.