A semiconductor processing device according to the invention includes a first non-volatile memory (21) for erasing stored information on a first data length unit, a second non-volatile memory (22) for erasing stored information on a second data length unit, and a central processing unit (2), and capable of inputting/outputting encrypted data from/to an outside. The first non-volatile memory is used for storing an encryption key to be utilized for encrypting the data. The second non-volatile memory is used for storing a program to be processed by the central processing unit. The non-volatile memories to be utilized for storing the program and for storing the encryption key are separated from each other, and the data lengths of the erase units of information to be stored in the non-volatile memories are defined separately. Therefore, the stored information can efficiently be erased before the execution of a processing of writing the program, and the stored information can be erased corresponding to the data length of a necessary processing unit in the write of the encryption key to be utilized in the calculation processing of the CPU.