A read and write box of a wireless tag reader and writer according to and embodiment of the invention has an open end and a closed end. Multiple envelopes each having a wireless tag at the end are inserted through the open end into the read and write box. The read and write box has a first read antenna and a second read antenna on the upper surface. The first read antenna detects wireless tags in a write area at the closed end; and the second read antenna detects wireless tags outside the write area. A write antenna is disposed at the closed end of the read and write box. The write antenna writes data to wireless tags. A step is formed on the lower surface of the read and write box in such a manner that the bottom of the write area is lower than the bottom adjacent to the open end so that the ends of the envelops align in the vicinity of the closed end.