1. A communication terminal apparatus comprising: a storage section configured to store a library function in which a first specific instruction is executed a process to be executed prior to a communication with a communication target and a second specific instruction is executed before returning to a call source, a client application, an attribute value group of the client application, and an permissible address range of the first specific instruction; a communication instruction execution control section configured to control execution of a communication instruction based on the attribute value group of the client application, when the client application executes the communication instruction to generate an internal interruption; a security gate entering section configured to check whether or not an address of the first specific instruction is within a permissible address range when the client application executes the first specific instruction to generate the internal interrupt, and to change the attribute value group of the client application when the address of the first specific instruction is within the permissible address range; and a security gate exiting section configured to return the attribute value group of the client application to an original state when the client application executes the second specific instruction to generate the internal interrupt.