This paper discusses feasibility of the high powered piezoelectric diaphragm pump used as the miniature actuator for industrial robot grippers. Utilization of high power and high response of piezoelectric elements for the pump is considered to realize the miniature actuator. Dynamic characteristics of the prototyped pump have been measured and analyzed. From experimental results of frequency responses of flow volume and output pressure and analytical results, it has been clarified that stiffness of the diaphragm against pressure in the pump greatly influences the performance of the pump.