A lost motion correction value setting method for a machine tool of a hybrid control system that performs a positional loop control with both machine position signals outputted from position detecting scales (9x and 9y) for detecting machine positions and motor position signals outputted from rotary encoders (7x and 7y) for detecting a rotational angle of a feed driving servomotor includes executing a test program; periodically inputting the machine position signals outputted from the position detecting scale and the motor position signals outputted from the rotary encoder; determining errors by determining the difference between the machine position signals and the motor position signals, determining the difference between an average value on an advance side and an average value on a return side of the errors, and storing the difference in lost motion correction value memories (19x and 19y) as a dynamic lost motion correction value.