According to an embodiment, a memory device includes a nonvolatile memory and a controller. The controller receives, from a host device, a write request for writing data in the nonvolatile memory, and then performs data writing based on the write request. When a writing order confirmation request, which is issued for confirmation of fact that data writing is performed based on one or more of the write requests that are already sent, is received from the host device, the controller performs data writing based on the write requests received before receiving the writing order confirmation request and then sends to the host device a response with respect to the writing order confirmation request.