An information requesting unit receives an information requesting signal sent to an information responding unit, at its own receiving port. The information requesting unit is provided with at least one of a power line anomaly deciding unit for deciding the short-circuit between a signal line and a power line in case the information requesting signal received at the receiving port is always fixed at an H (high) level, and a ground anomaly deciding unit for deciding the short-circuit between the signal line and the ground in case the information requesting signal received at the receiving port is always fixed at an L (low) level. This provision specifies either an abnormal portion of the signal line connecting the information requesting unit and the information responding unit in a digitally bidirectionally communicable manner or a cause for the anomaly.
COMMUNICATION ANOMALY DETECTING DEVICE, AND PASSENGER DETECTING DEVICE