Abstract: A data collecting system includes a data collecting device and plural data processing devices connected to the data collecting device by a cascade connection. For example, each of the data processing devices individually executes an A/D conversion and other data process, and adds data obtained by the data process to a data transmitting signal to transmit it to the subsequent cascade-connection data processing device in sequence. The data processing device at the head of the cascade connection generates the data transmitting signal including a data processing period and a communication period, and transmits it to the subsequent data processing device. Each of the data processing devices executes the data process in the data processing period, and transmits data obtained by the data process to the subsequent data processing device in the communication period on the basis of the data transmitting signal.