Abstract: A master device for calculating a synchronized actuation time for an N number of slave devices (N being an integer greater than or equal to 2) includes: a transmitting part configured to transmit a request message a K number of times (K being an integer greater than or equal to 2) to each of the N number of slave devices, where the request message includes an actuation command; a receiving part configured to receive a reply message from each of the N number of slave devices, where the reply message includes information on a K number of end-to-end delay times; and an absolute-time calculating part configured to calculate an absolute time for concurrently actuating the N number of slave devices by using the information on the K number of end-to-end delay times received from each of the N number of slave devices.