This invention is a method of determining set temperature trajectories for a heat treatment system that conducts a first heat treatment process and a second heat treatment process to an object to be processed. The method comprises the steps of: conducting the first heat treatment process to a first test object to be processed, by using a temporary first set temperature trajectory; measuring a result of the first heat treatment process produced on the first test object to be processed; and determining a first set temperature trajectory for the first heat treatment process by correcting the temporary first set temperature trajectory on the basis of the measured result of the first heat treatment process. The method also comprises the steps of: conducting the second heat treatment process to a second test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory, by using a temporary second set temperature trajectory; measuring a result of the first heat treatment process and the second heat treatment process produced on the second test object to be processed; and determining a second set temperature trajectory for the second heat treatment process by correcting the temporary second set temperature trajectory on the basis of the measured result of the first heat treatment process and the second heat treatment process.