A host device 200A includes a data buffer 250. When data has been already written to a part of a physical block and data is additionally written to the physical block, it is determined whether or not the data written to the physical block is held in the data buffer. When the data is held, data is written to the block, and when an error exists, data in unit of physical blocks is rewritten. When the data is not held in the data buffer, a new physical block is required to be secured and then, data is written to the new block. Thereby, even when power is shut off or an error occurs during writing in the semiconductor memory device, destruction of data already written is prevented.