To maximize a power consumption reduction effect in a case of using a high-efficiency induction motor, when a conventional induction motor is changed to a high-efficiency induction motor, a mechanical device including an induction motor and a speed reduction mechanism related to the present invention increases the reduction ratio of the speed reducer such that the rotation speed of the mechanical device is equal to that in a case of using a conventional induction motor and thus the output of the mechanical device is made equal to that in a case of using a conventional inductor motor; therefore, the load conditions of the mechanical device such as a pump and a fan can be made equal to those in a case of using a conventional induction motor. Accordingly, the power consumption reduction effect by improving the efficiency of the induction motor can be maximized.