To provide a transmission control system that can efficiently utilize communication bandwidth upon transmitting measurement data of machines. A transmission control system includes: a numerical control unit that controls operating of machines and acquires operating information; an A/C conversion unit that acquires behavior information measured by way of a sensor provided to the machine; a priority determination unit that determines priority of transmission in accordance with a condition set in advance, based on types and combinations of the operating information and the behavior information; and a bandwidth control unit that controls allocation of communication bandwidth for transmitting the operating information and the behavior information, based on a usage condition of communication bandwidth and the priority.