A management PC comprises a polling combination table 11a for storing data (combination data) where a combination of reader/writers, which are not problematic when being polled simultaneously, and a polled flag. The management PC examines combination data of each row by sequentially referencing the polling combination table starting at the first row in the polling process of a reader/writer. Then, one or a plurality of reader/writers set in the combination data are concurrently polled. Then, the polled flags of the polled reader/writers are set to “1”. After referencing the last row of the polling combination table, the management PC clears the polled flags of all of rows of the polling combination table to “0”, and repeats the above described series of operations.