PURPOSE: To execute a trap processing at a high speed by constituting a titled system so that an address of a task corresponding to a trap factor is obtained from a trap mapping table, by the contents of a trap vector table, with respect to a trap issued at the time of storage.

CONSTITUTION: When a trap of a supervisor call SVC, etc. is generated, in case the contents of a flag register 61 are "1", it is a trap from a secondary OS task 52, therefore, first of all, the contents of a program counter PC and a status register SR are saved to a stack which is being used at present. Thereafter, the contents of a trap mapping table 63 of an address shown by a pointer register 62 are referred to directly without executing a processing for referring to an address of an interruption vector table 51-1, which is executed by a conventional technique. Subsequently, a control shifted directly to an address of a trap processing task corresponding to a trap factor is executed.