According to one embodiment, a memory system includes a semiconductor memory and a controller. The semiconductor memory includes blocks each containing memory cells. The controller is configured to instruct the semiconductor memory to execute a first operation and a second operation. In the first operation and the second operation, the semiconductor memory selects at least one of the blocks, and applies at least one voltage to all memory cells contained in said selected blocks. A number of blocks to which said voltage is applied per unit time in the second operation is larger than that in the first operation.