1. A data processor comprising: a memory for storing instructions; an instruction fetch unit for fetching the instructions from said memory; an instruction decoding unit for decoding the instructions fetched by said instruction fetch unit; an instruction execution unit for executing the instructions on the basis of the instruction decoding result by the instruction decoding unit; and pre-jump means including, a jump target address generating unit having means for generating the jump target address relating to processing the jump instruction, and transferring means for transferring said jump target address to said instruction fetch unit, and means for, at jump instruction processing, instructing to fetch an instruction of the jump target by transferring the jump target address generated in said jump target address generating unit to said instruction fetch unit via the transferring means; and a mode register for, which can be set by the instruction or hardwares, specifying operation modes; wherein at processing the unconditional jump instruction, said pre-jump means generates said jump target address in said jump target address generating unit, and transfers said jump target address to said instruction fetch unit via said transferring means, and said instruction fetch unit fetches an instruction of said jump target, when said mode register shows a first mode, said unconditional jump instruction is processed in said instruction execution unit, and when said mode register shows a second mode, said unconditional jump instruction is not processed in said instruction execution unit.