Information processing system and information processing method for executing instructions in parallel

An information processing apparatus in which instructions are processed one by one conceptually and results thereof are conceptually orderly written into a memory comprises an instruction control circuit capable of decoding M instructions and reading operands in parallel, N (N>/=M) execution circuits capable of executing a plurality of instructions mutually in parallel, a detection circuit for determining whether all of M execution circuits of the N execution circuits required by the M instructions decoded by the instruction control circuit are vacant or not, and a reserve circuit for reserving the execution of the M decoded instruction while the detection fails to detect sufficient vacancy.