A motor control device is a motor control device which controls a spindle motor of a machine tool, the device including: a low-pass filter which averages torque command values or drive current values of the spindle motor and calculates averaged load information of the spindle motor; and a time constant calculation unit which calculates, as a time constant of the low-pass filter, a first time constant based on a cut-off frequency according to the rotation number of the spindle driven by the spindle motor, or a second time constant based on a cut-off frequency according to a value produced by multiplying a of cutting tooth number of a tool by the rotation number of the spindle.