To read and write an amount of content in a container through one antenna even when the amount is increased during a period in which a large amount of items to be washed having wireless tags are to be transferred and managed by the container.

A wireless tag reading device is constructed such that a container 1 for storing items having wireless tags 3 to be washed is provided with a slit 8 so as to divide a storing region of the container 1 and at the same time the container 1 is transferred by a belt conveyor 7 with the slit 8 being faced in a transferring direction. Then, a reading/writing device 5 reads out and writes information from the wireless tag 3 of each of the items to be washed stored in the container 1 when the slit 8 of the container 1 passes by a position of a plate-like antenna 2.