In a master unit, clock signals from a clock are counted by a counter, and clock data is generated. This clock data is outputted to a slave unit by a driver, and stored in clock data storage memory. The slave unit stores clock data received by a receiver in the clock data storage memory. A processor for a program controller of the master and slave units starts up, and executes the synchronized operation of an operating program of axes that are synchronized on the basis of clock data stored in the clock data storage memory. It is also possible to commence operation of an axis under other conditions without relying on clock data. If override is applied to clock data, override will apply only to an axis that is synchronized and operated in accordance with clock data.