PURPOSE: To change freely an interrupt processing program by providing identifying flags corresponding to interrupt causes and controlling these flags.

CONSTITUTION: An identifying register 3 has a section 1 set to "1" by a selective entering circuit 6 so that an interrupt processing program is started when an interrupt cause 1 is generated. If an interrupt due to an interrupt cause 0 is generated, an interrupt cause decoder 5 enters "1" in a section 0 of a register 2, and therefore, an exclusive OR EOR arithmetic circuit 4 outputs "1" to start an interrupt processing program A. However, if the interrupt cause 1 is generated, the EOR arithmetic circuit 4 outputs "0" and a program selecting part 7 starts the interrupt processing program B becuase "1" is entered in the section 1 of the register 2. That is, one interrupt processing program B is started selectively only when a specific interrupt cause is generated.