A memory system includes a nonvolatile semiconductor memory, and a controller circuit that includes a physical layer and is configured to store information defining a plurality of low power consumption modes for setting the physical layer to a low power consumption state while controlling the physical layer according to a first standard, and control input and output of signals between the physical layer and the nonvolatile semiconductor memory according to a second standard. The controller circuit selects one of the low power consumption modes based on a data transfer state of the physical layer.