A numerical control system improves safety when asynchronously operating systems are operated as a single control unit. A machine control system outputs a command generated by interpreting a program with a command number assigned thereto, sends it to a collision detection system, and receives check result data therefrom, whereby when the number of commands for which check result data are obtained is more than or equal to a preset second threshold, a command number assigned to the check result data is output when it is determined that there is no probability of collision. When the result of a check on the probability of collision for a command received from a linkage data sending and receiving section is returned, the collision detection system returns check result data to the linkage data sending and receiving section by assigning a command number given to the checked command to the check result data.