A digital signal processor is adapted to a working RAM, which is capable of storing a plurality of data in a rewritable manner and whose storage area is divided into a plurality of sub-areas that are designated by addresses in read/write operations, wherein an operation circuit performs calculations on the data of the working RAM in accordance with a program, and wherein upon detection of a non-access event in which the program does not need to access the working RAM, a write circuit compulsorily writes `0` into the working RAM with regard to each of the prescribed addresses of the prescribed sub-areas subjected to initialization, which are designated by address data. Thus, it is possible to actualize the selective initialization on the prescribed sub-areas within the working RAM without increasing the scale of the peripheral circuitry, without requiring complicated controls, and without increasing the overall processing time therefor.