A numerical control system exchanges input/output signals between a numerical controller and an IO unit and the IO unit includes a first control unit that changes an idle signal output from the IO unit using an input signal as a trigger to a specific waveform pattern signal and when the specific waveform pattern signal is received, transmits the specific waveform pattern signal to a former side. The numerical controller includes a second control unit that outputs an interrupt signal when the specific waveform pattern signal is received.