When braking of a motion of a part of a first robot is assumed to be started at points in time, a first stop position of the first robot part is estimated at each point in time. When braking of a motion of a part of a second robot is assumed to be started at the points in time, an estimated second stop position of the second robot part is obtained at each point in time. When it is determined that the first stop position of the first robot part at one of the points in time and either the actual position or the second stop position of the second robot part for each interval at the one of the points in time are contained in the shared workspace, the first robot part is braked.