PURPOSE: To secure secrecy of ROM data by providing a security code cell array in a storing cell array and allowing reading out stored data for only a person who knows a security code.

CONSTITUTION: When external 4 bits data and data detected by a security code cell array 11 are the same as each other, the value of a counter 20 is increased by 1, a DFF 18 is kept in a state in which it is set to '1'. However, when the external 4 bit data are unequal to 4 bit data detected by the array 11 as a result of comparison, the value of the counter 20 is not increased, the DFF output is made '0'. This '0' state is inputted to a fuse section 19 to out the fuse and maintains the input of a HAND gate in an output driving section 10 receiving the output of a fuse section 19 permanently in a low state. Thereby, data to a storing memory cell array can not be read out without knowing a security code cell array data.