A communication system comprising: a superior control device; a first subordinate control device (31 to 34) capable of communicating with the superior control device via a first bus; and a second subordinate control device (41 to 44) capable of communicating with the superior control device via a second bus, wherein the superior control device includes a first transmission unit configured to periodically transmit, to the first bus and the second bus, a count signal including a count value counted up every time the count signal is transmitted, and a second transmission unit configured to transmit a control signal including a start count value and control content to the first bus and the second bus, wherein a transmission priority of the count signal is set to be higher than a transmission priority of the control signal, wherein the first subordinate control device (31 to 34) and the second subordinate control device (41 to 44) include a first reception unit (31 to 34, 41 to 44) configured to receive the count signal, and a second reception unit (31 to 34, 41 to 44) configured to receive the control signal, wherein after the control signal is received, when the count value included in the received count signal becomes equal to the start count value included in the control signal, an operation corresponding to the control content included in the control signal is started, and wherein the superior control device causes the control signal to include the start count value having a shorter difference from the count value included in the count signal transmitted immediately before as the transmission priority of the control signal is higher, and transmits the control signal. a superior control device; a first subordinate control device (31 to 34) capable of communicating with the superior control device via a first bus; and a second subordinate control device (41 to 44) capable of communicating with the superior control device via a second bus, wherein the superior control device includes a first transmission unit configured to periodically transmit, to the first bus and the second bus, a count signal including a count value counted up every time the count signal is transmitted, and a second transmission unit configured to transmit a control signal including a start count value and control content to the first bus and the second bus, a first transmission unit configured to periodically transmit, to the first bus and the second bus, a count signal including a count value counted up every time the count signal is transmitted, and a second transmission unit configured to transmit a control signal including a start count value and control content to the first bus and the second bus, wherein a transmission priority of the count signal is set to be higher than a transmission priority of the control signal, wherein the first subordinate control device (31 to 34) and the second subordinate control device (41 to 44) include a first reception unit (31 to 34, 41 to 44) configured to receive the count signal, and a second reception unit (31 to 34, 41 to 44) configured to receive the control signal, wherein after the control signal is received, when the count value included in the received count signal becomes equal to the start count value included in the control signal, an operation corresponding to the control content included in the control signal is started, and wherein the superior control device causes the control signal to include the start count value having a shorter difference from the count value included in the count signal transmitted immediately before as the transmission priority of the control signal is higher, and transmits the control signal.