A microcomputer includes a CPU capable of performing a plurality of tasks in a parallel time-sharing operation. The tasks include at least one special task having a fixed loop program with a constant increase of an instruction address. When the CPU performs a conditional judgment instruction in the special task, the CPU prohibits reflecting an execution result of the conditional judgment instruction to both of the CPU and a periphery circuit in a case where it is no need to perform an instruction described in the special task after the conditional judgment instruction.