1. A storage apparatus comprising: a memory configured to have a plurality of pages to which data can be written in units of a page, said memory being further configured to have a plurality of pages of write data stored into each page in multi-valued form; and a control section configured to select pages to which to write the data from among said plurality of pages of said memory, said control section being further configured to write to the selected pages of said memory the data of at least two bits in multi-valued form for a plurality of pages including the selected pages; wherein, when writing said plurality of pages of said write data, said control section puts said write data into multi-valued form per page before writing the data to a plurality of different unused pages of said memory on a page-by-page basis.