PURPOSE: To avoid the contention between count-up of packet information and an access of a control means and to prevent missing or asynchronization of the packet information in advance.

CONSTITUTION: A storage means 4 is provider with storage areas 4a, 4b. A packet information control means 2 inputs packet information, generates an address and outputs it to a selection means 6, which selects either of the storage areas 4a, 4b to store the packet information to the selected storage area. When the control means transfers an access signal to the selection means 6 to select the storage, area 4a or 4b in the standby state, since a control signal is outputted from the selection means 6, a selection means 7 selects the other storage area other than the storage area selected by the selection means 6 and transfers an access enable signal to the control means 5.