To provide a semiconductor storage device having an enhanced security function for not only read data but also write data.

The semiconductor storage device is provided with: a memory equipped with a data storage part for storing data and a key code storage part for storing a key code to be successively updated; a data scrambling circuit for reading the data stored in the data storage part, and for encrypting the data according to a data scrambling key code, and for outputting the data; a data descrambling circuit for decrypting the encrypted and input data according to a data descrambling key code, and for writing the data in the data storage part; a pseudo random number generation circuit for generating a pseudo random number corresponding to a first key code extracted from the key code storage part as a second key code, and for supplying it to the data scrambling circuit, and for supplying it to the data descrambling circuit; and an arithmetic circuit for preparing a third key code by calculating the first key code and the second key code, and for updating the first key code with the third key code by writing it in the key code storage part.