A communication apparatus for transmitting and receiving information to and from an external device (302, 303, 305) through a communication line (111, 306), the communication apparatus comprising: register processing means for registering, in a storage unit, an IP address, input by a user, of an external device (302, 303, 305) as a first IP address usable to refuse reception or to permit reception from the external device; obtaining means for obtaining, based on the first IP address registered in the storage unit, an additional IP address of the external device (302, 303, 305) indicated by the first IP address registered by said register processing means; additional register processing means for registering, in the storage unit, the additional IP address obtained by said obtaining means in association with the first IP address; determination means operable, upon receipt by the communication apparatus of information transmitted thereto by an external device (302, 303, 305), to determine whether or not an IP address of the external device (302, 303, 305) concerned matches with the first IP address stored in the storage unit and to determine whether or not the IP address of the external device concerned matches with the additional IP address stored in the storage unit; filtering control means operable to refuse or permit reception of such transmitted information from the external device (302, 303, 305) concerned based on a result of the determination by said determination means; and log storage means for storing a log of destination IP addresses and MAC addresses from past communication through the communication line (111, 306), wherein said obtaining means, in a case that the additional IP address of the external device (302, 303, 305) indicated by the registered first IP address is stored in said log storage means, obtains the additional IP address from said log storage means. register processing means for registering, in a storage unit, an IP address, input by a user, of an external device (302, 303, 305) as a first IP address usable to refuse reception or to permit reception from the external device; obtaining means for obtaining, based on the first IP address registered in the storage unit, an additional IP address of the external device (302, 303, 305) indicated by the first IP address registered by said register processing means; additional register processing means for registering, in the storage unit, the additional IP address obtained by said obtaining means in association with the first IP address; determination means operable, upon receipt by the communication apparatus of information transmitted thereto by an external device (302, 303, 305), to determine whether or not an IP address of the external device (302, 303, 305) concerned matches with the first IP address stored in the storage unit and to determine whether or not the IP address of the external device concerned matches with the additional IP address stored in the storage unit; filtering control means operable to refuse or permit reception of such transmitted information from the external device (302, 303, 305) concerned based on a result of the determination by said determination means; and log storage means for storing a log of destination IP addresses and MAC addresses from past communication through the communication line (111, 306), wherein said obtaining means, in a case that the additional IP address of the external device (302, 303, 305) indicated by the registered first IP address is stored in said log storage means, obtains the additional IP address from said log storage means.