Gravity wave (GW) activities around the subtropical jet of the Southern winter (June) are analyzed using Atmospheric General Circulation Model outputs of T106L60, in order to clarify roles of GWs in maintaining the zonal mean zonal wind. Dominant GWs are characterized with periods of 10--24 hours relative to the ground, and with horizontal and vertical wavelengths of about 600--700 km and 2.2--4.4 km, respectively. These GWs propagate both upward and downward from the jet, and westward relative to the mean zonal wind. Most of the upward propagating waves do not reach the upper stratosphere due to negative vertical wind shear of the zonal wind in the lower stratosphere. Dominant upward fluxes of easterly momentum due to the non-stationary GWs extend zonally along 30¿S above the jet. Remarkable EP-flux convergence due mostly to these GWs is seen around 100 hPa at 30¿S, and explains up to 30% of the total EP-flux convergence.