A numerical controller for controlling a machine tool for machining a work on the basis of an NC program for execution including a variable includes NC program reading unit, NC program analyzing unit, and a variable value table sequentially holding a variable value assigned to a variable at time of execution of a predetermined unit of program read by the NC program reading unit, and the NC program analyzing unit includes a character string for variable-check creating unit for replacing a character string included in an instruction affected by the variable in the predetermined unit of program with a character string for variable-check on the basis of the predetermined unit of the program read by the NC program reading unit and the variable value obtained from the variable value table and an NC program for variable-check writing unit.