Numerical control system having synchronous control function between units

A numerical control system comprising a master unit and a slave unit that perform numerical control and are connected by a communication path, wherein, for performing synchronous control between the master unit and the slave unit, the master unit periodically transfers synchronization information to the slave unit and, on the other hand, the slave unit performs the synchronous control based on the synchronization information transferred from the master unit, wherein

• the slave unit includes
• a reception time acquiring section for acquiring a reception time of the synchronization information,
• a reception time recording section for recording a history of the reception time of the synchronization information, as reception time history data,
• a retransmission detection section for detecting retransmission of transfer of the synchronization information, and
• a reception time correcting section for correcting the reception time of the synchronization information based on the reception time history data when the retransmission detection section detects the retransmission of the transfer of the synchronization information, and wherein
• the slave unit is configured to perform the synchronous control based on the reception time corrected by the reception time correcting section.