Disclosed is a numerical controller that has a cutting in/out motion inserting function and configured to control a machine tool that performs lathe-turning machining in which a cutting tool moves in contact with a rotating workpiece. The numerical controller includes a cutting in/out motion inserting unit that generates a program to perform cutting in/out motion, based on operation conditions analyzed by a cutting in/out motion operation conditions analysis unit and inserts the generated program of performing the cutting in/out motion to a program to perform the lathe-turning machining.