The author found that an internal flow did not necessarily show the bi-stability which is indispensable in fluid logic devices. The existence of bi-stability depended on the splitter arrangement, which, at times, produced an almost periodic oscillation. The author investigated the splitter arrangement systematically and found the oscillating condition. In this paper, velocity fluctuation in the output port is measured by a hot wire anemometer and the output signals are recorded on the floppy discs of a personal computer after analog-to- digital conversion. Power spectrum analyses by FFT are applied to those records, and aspects of oscillating phenomenon are experimentally clarified. In order to load in the output ports, both ports are blocked by throttle plates with knife-edged ends and the extent of the load is estimated by a coefficient of wall static pressure.