A piezo-electric transducer type pressure sensor such as a silicon pressure sensor or the like is provided in a low path of fluid located in the midway between a valve section and a nozzle ejection port in a fluid ejection gun. When foreign matters in the fluid block the nozzle and hence the ejection from the nozzle becomes an abnormal condition, a fluid pressure variation produced in the flow path between the valve section and the nozzle ejection port is detected in the form of an electric signal by means of the piezo-electric transducer type pressure sensor.