1. A scheduling method for scheduling tasks providing a system designed on an object-oriented basis by using a computer, comprising: a first step of extracting classes forming said system from design information of the system, generating tasks corresponding to the extracted classes, and storing information on the generated tasks into a given storage device; a second step of extracting complexity of the classes from the design information of said system, estimating workload required for implementation of the classes on the basis of the complexity, and storing a result of the workload estimation into the given storage device; and a third step of scheduling the tasks on the basis of the information on the tasks stored in said given storage device and the result of the workload estimation, wherein in said second step, past workload achievements in each class are used to estimate the workload of the classes.