An object is to provide a numerical control system of a machine tool which can check a parameter that needs to be adjusted for each of a spindle and a motor. A numerical control system of a machine tool includes a parameter check function unit for checking a drive control parameter of a spindle, and the parameter check function unit includes: an acceleration/deceleration time measurement unit which measures an acceleration/deceleration time that elapses after the spindle receives an acceleration command and/or a deceleration command until the completion of acceleration and/or the completion of deceleration; an acceleration/deceleration time specified value storage unit which stores a specified value of the acceleration/deceleration time that is previously determined for each specification of the machine tool; and a determination unit which compares the acceleration/deceleration time measured with the acceleration/deceleration time measurement unit and the specified value stored in the acceleration/deceleration time specified value storage unit so as to determine whether or not the drive control parameter of the spindle is proper.