A convergence determination unit determines whether a state of the bucket has converged to a current target state. A target state update unit is configured to update a target state of the bucket when the convergence determination unit determines that the state of the bucket has converged to the current target state. The convergence determination unit includes a first convergence determination unit and a second convergence determination unit. The first convergence determination unit determines whether a swing angle of each mechanism has converged to the corresponding target swing angle under a first convergence condition. The second convergence determination unit determines whether a swing angle of each mechanism has converged to the corresponding target swing angle under a second convergence condition, which is stricter than the first convergence condition.