A data collection system includes a subordinate controller configured to control an electrical device, and a superordinate controller connected to the subordinate controller via synchronous communication and asynchronous communication to control the subordinate controller. The superordinate controller includes a reference signal transmitter to transmit a timing reference signal to the subordinate controller via the synchronous communication. The subordinate controller includes data storage configured to record data relating to the electrical device; a delay time calculator to measure a delay time from a timing at which the subordinate controller receives the timing reference signal to a timing at which the data storage starts recording the data; and a data transmitter configured to transmit the data and the delay time to the superordinate controller via the asynchronous communication or the synchronous communication.