A processor, comprising: an instruction supply means for supplying a plurality of instructions, each instruction including information specifying the instruction's operation and execution condition information specifying a condition indicating whether the instruction is executed; a decoding means for decoding the plurality of instructions; an instruction issue control means which references the condition specified by the execution condition information to determine an instruction or a set of instructions whose valid operation is executed; and an execution means for executing one or a plurality of operations based on the information specifying the operation of the instructions, wherein the instruction issue control means has the function to decide, by referencing the condition specified by the execution condition information, whether an instruction is a valid instruction that needs to be executed or an invalid instruction that does not need to be executed, to cause the deletion of an instruction that has been decided to be an invalid instruction before it is issued to the execution means, and to issue a valid instruction following that invalid instruction to the execution means instead of the invalid instruction; and an execution result invalidation means for invalidating an execution result after the execution means has executed an operation corresponding to said instruction; and characterized in that an instruction invalidation method selection means for selecting for each instruction whether that instruction is deleted before it is issued to the execution means, or whether its execution result is invalidated by the execution result invalidation means, wherein the instruction invalidation method selection means selects one of the instruction invalidation methods by referencing condition flag validity information that indicates whether the values of condition flags have been finalized; and wherein in the condition flag validity information, if the decoding means has decoded an instruction that updates a condition flag, then the finalization of that condition flag is set to false, and when the execution means has executed that instruction and the value of its condition flag has been finalized, then the finalization of that condition flag is set to true. an instruction supply means for supplying a plurality of instructions, each instruction including information specifying the instruction's operation and execution condition information specifying a condition indicating whether the instruction is executed; a decoding means for decoding the plurality of instructions; an instruction issue control means which references the condition specified by the execution condition information to determine an instruction or a set of instructions whose valid operation is executed; and an execution means for executing one or a plurality of operations based on the information specifying the operation of the instructions, wherein the instruction issue control means has the function to decide, by referencing the condition specified by the execution condition information, whether an instruction is a valid instruction that needs to be executed or an invalid instruction that does not need to be executed, to cause the deletion of an instruction that has been decided to be an invalid instruction before it is issued to the execution means, and to issue a valid instruction following that invalid instruction to the execution means instead of the invalid instruction; and an execution result invalidation means for invalidating an execution result after the execution means has executed an operation corresponding to said instruction; and characterized in that an instruction invalidation method selection means for selecting for each instruction whether that instruction is deleted before it is issued to the execution means, or whether its execution result is invalidated by the execution result invalidation means, wherein the instruction invalidation method selection means selects one of the instruction invalidation methods by referencing condition flag validity information that indicates whether the values of condition flags have been finalized; and wherein in the condition flag validity information, if the decoding means has decoded an instruction that updates a condition flag, then the finalization of that condition flag is set to false, and when the execution means has executed that instruction and the value of its condition flag has been finalized, then the finalization of that condition flag is set to true. an instruction invalidation method selection means for selecting for each instruction whether that instruction is deleted before it is issued to the execution means, or whether its execution result is invalidated by the execution result invalidation means, wherein the instruction invalidation method selection means selects one of the instruction invalidation methods by referencing condition flag validity information that indicates whether the values of condition flags have been finalized; and wherein in the condition flag validity information, if the decoding means has decoded an instruction that updates a condition flag, then the finalization of that condition flag is set to false, and when the execution means has executed that instruction and the value of its condition flag has been finalized, then the finalization of that condition flag is set to true.