A controller controls a machine tool that rotates a cutting tool attached to a spindle to cut a workpiece in accordance with a machining program. The controller identifies, when the machining program is executed to cause the cutting tool to cut into the workpiece, a position where the cutting tool has come into contact with the workpiece for the first time and a machining direction at the time when the cutting tool has cut into the workpiece, and inserts, in the machining program, a roll-in path instruction having an end point set to the identified position at which the cutting tool has come into contact with the workpiece for the first time.