According to one embodiment, there is provided a memory system including a volatile memory and a controller. The volatile memory has 1st to Kth memory banks (K is a natural number equal to or larger than 2) that are kept in a power-on state and (K+1)th to Nthmemory banks (N is a natural number larger than K) whose power state is changed. The power state is the power-on state or a power-down state. The controller performs wake-up operation for the (K+1)th to Nth memory banks in parallel with access operation to the 1st to Kth memory banks. The wake-up operation changes the power state from the power-down state to the power-on state.