Provided are a synchronization control section that executes a current thread and a reference thread in parallel, a waiting time calculation section that calculates the time needed for the reference thread to reach a second synchronization point as a waiting time of the current thread when the reference thread does not reach the second synchronization point at a time when the current thread reaches a first synchronization point, a quality difference calculation section that estimates a quality difference between data that the current thread generates by referring to processing data at the second synchronization point of the reference thread and data that the current thread generates without referring to the processing data, and a synchronization determination section that determines whether to make the current thread wait until the reference thread reaches the second synchronization point depending on the waiting time and the magnitude of the quality difference.