There are provided a motor control device and a method for deciding a velocity instruction shape within the limit of a movement range, a velocity, and an acceleration of an object device while maintaining the acceleration as high as possible in inertia identification. The motor control device includes a position control unit for generating a velocity instruction based on a position instruction and a motor position, a velocity control unit for generating a torque instruction based on the velocity instruction and a motor velocity, and a motor drive unit for generating motor current from the torque instruction. The motor control device further includes a model control unit for generating a model torque instruction based on the velocity instruction and a model velocity, an inertia identification unit for identifying an inertia from a predetermined positional instruction according to a ratio of the motor torque instruction integrated value obtained by temporal integration of the torque instruction of the motor at a predetermined section and the model torque instruction integrated value obtained by temporal integration of the model torque instruction at a predetermined section, and an instruction shape generation unit for automatically generating an instruction shape upon identification according to the conditions of the maximum movable distance, the permitted velocity, the permitted acceleration, and the maximum operation time of the object machine.