A two-dimensional jet is a basic, free shear flow. The analytical solution of velocity for a laminar tow-dimensional jet was given by Bickley. The critical Reynolds number of the two-dimensional jet was obtained using linear stability theory and its value is approximately 20. However, it is very difficult to conduct the experiment on the jet flow at very low Reynolds numbers. We deal with the two-dimensional jet within the range of Reynolds number from 10 to 100. A pump was newly made to control the small flow rate accurately by a stepping motor. Flow visualization by smoke and velocity measurement by the hot wire anemometer are tried using the pump. From flow visualization of the jet flows, it is expected that the critical Reynolds number is between 30 and 40. Mean velocity profiles are in agreement with Bickley's profile.
