Pulse Ultrasonic Doppler method for flow metering system has being developed. The principle is an integration of instantaneous velocity profile over a pipe diameter so that it is expected to be able to eliminate installation problems such as entry length as well as to follow transient flow rate precisely. Flow metering principle by pulse ultrasonic Doppler method in a circular pipe depends on the alignment of measuring lines. In most cases metallic pipes are used at power plant and other plants. This system has been developed to be applied for conventional piping system of metallic wall [1] [2]. Laboratory experiments have shown a very good agreement with the flow rate measurement using conventional orifice flow meter. Additionally, it shows a good tractability for transient behavior. In order to establish the technique and investigate its absolute accuracy, the comparison among experimental results has been performed at the NIST calibration stand [3]. On the other hand, reflectors are needed for flow rate measurement using Pulse Ultrasonic Doppler method, and it's not easy to seed the water with some particles at power plants. In this paper, influence of number of measuring lines and the difference of some metallic pipes on the flow rate measurements have been investigated for non-developed flows in a vertical pipe. And for reflectors ultrasonic cavitations bubbles have been applied. [1] Kikura, H., et al., Proc. of 3^<rd> ASME/JSME Joint Fluid Engin. Conf. (1999), FEDSM99-7141. [2] Mori, Metallic., 7th Int. Conf. on Ncl. Engin. (ICONE7), Tokyo (1999), ICONE-7429. [3] Takeda, Y., et al., ASME 2000 Fluids Engn. Divi. Summer Meet., (2000), FEDSM2000-11102