A main Central Processing Unit (CPU) controls enabling and disabling a function of a network filter, and disables a function of a packet type filter (Transmission Control Protocol (TCP) header filter) during a ready status after a system is powered on. The packet type filter whether a predetermined flag corresponds to a flag included in a TCP header of an Internet Protocol (IP) packet received through a network. The main CPU enables the function in an energy-saving mode, and disables the function when the energy-saving mode transitions to the ready status.