An apparatus acquires a packet transmitted according to a protocol employing block access, from a communication network, and determines which one of a system attribution block storing stores file system attribution data, a file attribution block storing file attribution data, and a file name block storing file name data the packet is related to. The apparatus calculates a block number of the file attribution block, based on addresses provided to the system and file attribution blocks, when the packet is determined to be related to the file attribution block. The apparatus calculates an identification number of each piece of the file attribution data, based on the system attribution data and the calculated block number, and associates file attribution data stored in the file attribution block with file name data stored in the file name block, based on the calculated identification numbers and identification numbers provided to the file name data.