A digital signal processing unit includes a control unit and a data computing unit. An R/L register for distinguishing independent data is disposed in the control unit. An R/L select signal for indicating independent data is supplied to the data computing unit. A data processing instruction signal for distinguishing a data processing instruction from other instructions is issued from an instruction decoder. The R/L register for distinguishing independent data is controlled by the data processing instruction signal. In the data computing unit, the portion related to storing independent data is multiplexed according to the number of independent data to be processed, and this multiplexed portion is controlled by the R/L select signal supplied from the control unit.