disclosed is a tamper resistant pin entry apparatus for input of a key and for encryption of a password in a cash transaction machine . the pin entry apparatus supplies the electric power to a memory of an electric circuit section , in such a manner that a first rod and a second rod of a rear case connect contacts of a key scan board , wherein the first rod is protruded on the rear of a key module including a button provided substantially on the front of the key module and the second rod of the rear case is coupled with the rear of the key module . at this time , in case that the rear case is removed from the key module or damaged , thereby changing the location of any one of the first and the second rods at the contact , the electric circuit section detects the event and destroys the memory itself physically . otherwise , the electric circuit section makes information stored in the memory physically or softwarely unreadable , thereby preventing the leakage of the information .