Bill identification and counting machine

The states of various sensors and actuators of a bill identifying/counting machine are stored at regular time intervals in a ring memory. If the identifying/counting machine makes an error, among the stored data, the data concerning the error is associated with the error event and the data and the error event are stored together in a nonvolatile memory or a hard disk. Later, the data is extracted and the error is analyzed. Specifically, after the power is turned on or counting is started, digital port input/output information (the states of the sensors and actuators), the analog sensor voltages, and the motor current values are stored at regular time intervals in a memory. If an abnormality occurs, the stored port information and voltages together with the abnormality content are stored in a nonvolatile memory.