A short cell multiplexer includes a sequence designating unit, in which reading intervals corresponding to QOS classes are set in respective reading interval setting registers. A counter memory is stored with the number of timings at which the short cells can be read. The sequence designating unit specifies the QOS class in which the number of timings reaches the reading interval on the basis of the reading interval and the number of timings, and gives to a reading unit an indication of reading the short cell belonging to this class.