To protect dialing or personal information without utilizing an exchange when a portable telephone is lost by locking the reading of those data when a caller's telephone number included in an incoming signal is matched with a previously stored locking telephone number.

The telephone number of a telephone set fixed in a home, e.g. is stored in lock processing No.411 stored in a 1st memory 41 as a locking telephone number. A caller's telephone number incoming through a base station is matched with the lock processing No.411, a control processing part 11 drives a timer 33 and starts calling tone processing to count time up to user's off hook. When the count value reaches previously determined off hook time, the processing part 11 executes the lock processing and ends the operation. When off hook is executed by a user, the processing part 11 displays a message for requesting the input of an identification(ID) number, and when an inputted ID number is matched with a previously stored ID number 413, unlocks the locked state. But when both the ID numbers is not matched with each other, the operation is ended.