A contents processing device permitting, when contents are to be stored in a recording medium, only a specified device to read out the stored contents is to be provided, and a contents processing device capable, where it is a mobile telephone, of flexibly adapting to a change of a unique telephone number or a type of the mobile telephone. For the purpose, the contents processing device for inputting and outputting contents to and from a recording medium is provided with contents storage means (RAM) for storing contents, an ID storage unit (ROM) for storing an ID capable of identifying the contents processing device, a recording medium input/output unit (memory card I/F) for inputting to and outputting from the recording medium, and a ciphering unit (ciphering program) for enciphering contents within the contents storage unit by use of a ciphering key generated from the ID within the ID storage unit and storing it from the recording medium input/output unit into the recording medium.