A machine learning device includes a state observation unit for observing state variables that include at least one of the state of an assembly constituted of first and second components, an assembly time and information on a force, the result of a continuity test on the assembly, and at least one of position and posture command values for at least one of the first and second components and direction, speed and force command values for an assembly operation; and a learning unit for learning, in a related manner, at least one of the state of the assembly, the assembly time and the information on the force, the result of the continuity test on the assembly, and at least one of the position and posture command values for at least one of the first and second components and the direction, speed and force command values for the assembly operation.