In a method for processing a workpiece in a tool machine, a first step (Step S4) for continuously measuring a position of a tip portion of a tool attached to a main axis, a second step (Step S5) for computing a displacement amount of the position of the tip point of the tool based on a result of the measurement, a third step (Step S8) for observing a time period while the displace amount is belonged in arrange of allowable displace amount previously determined, a fourth step (Step S9) for keeping an idling operation in case that the time for which the displace amount is belonged in the range of the allowable displacement amount is shorter than a time period previously determined and intermitting the idling operation in the case that the time for which the displace amount is belonged in the range of the allowable displacement amount become the time period previously determined and a fifth step (Step S10) for starting a process with respect to the workpiece in the case that the idling operation is finished are operated in order.