1. A portable radio terminal comprising: means for storing only a predetermined number of received messages, means for deleting the oldest-message among messages having no protection attribute when the number of messages exceeds the predetermined number, means for changing the protection attribute of the message, means for detecting a protection attribute having been provided to a message having no protection attribute while the number of messages having a protection attribute is equal to the maximum protection number, means which, upon detection of execution of a protection-attribute assignment operation with regard to a message having no protection attribute while the number of messages having a protection attribute is equal to the maximum protection number, sequentially displays only messages having a protection attribute in response to actuation of a selection switch, and means which, upon detection of a determination switch being pressed while a message having a protection attribute is displayed as a message whose protection attribute is canceled, cancels the protection attribute of the message thus displayed.