A controller for a machining-device includes a control-unit. The control-unit sequentially repeats a tapping step of tapping at a tapping-position by moving a tool from a retracted-position to a depth-position while rotating the tool in a normal direction, a retracting step of retracting the tool by moving from the depth-position to the retracted-position while rotating the tool in a reverse direction, and a positioning step of positioning a subsequent tapping-position. The control-unit performs a process including starting the positioning step at the same time as when the tool passes a reference-position in the retracting step, completing the positioning step at the same time as when the tool passes the reference-position in the tapping step, and controlling a timing at which acceleration of a workpiece and the tool finishes in the tapping step and a timing at which deceleration of the workpiece and the tool starts in the retracting step.