The gas entrainment characteristics of an ejector fitted with a straight-type throat was investigated experimentally using a horizontal flow liquid jet. The gas entrainment rate of the horizontal flow liquid jet increased with increase in liquid flow rate and throat diameter. The entrainment rate was shown as a function of power input per unit volume of liquid and throat diameter. The empirical correlation obtained in this work can be predicted by the observed values of the entrainment rate within an error of +/-20%. The relationship between the driving pressure and the operating conditions was investigated in the case of single nozzles. As a result, an empirical correlation by which the observed values of the motive pressure can be predicted within an error of +/-5% was obtained.