A first program obtains calculation resource information for determining computer calculation resource to be used by one of a plurality of second programs, one to be begun being executed by the computer, and releases, based on the calculation resource information obtained, a part of the computer calculation resource currently used by the first program. A second program is executed, using the released computer calculation resource. An information processing system comprises a parallel execution condition information obtaining unit for obtaining parallel execution condition information indicating condition of one of the plurality of second programs, one to be executed in parallel to the first program, the condition being set according to the first program and, and an execution restricting unit for restricting execution of a part or all of the plurality of second programs, based on the parallel execution condition information.