A swirler with a fuel manifold, and a combustor and gas turbine including the same are provided. The swirler may include a swirler body disposed between an inner surface of a fuel nozzle and an outer surface of a center body, a fuel injection hole disposed on the swirler body, a fuel manifold formed in the swirler body, the fuel manifold being connected to a fuel channel disposed in the center body while communicating with the fuel injection hole, and a turbulence alleviator formed at a fuel inlet of the fuel manifold to alleviate creation of turbulence of fuel flowing from the fuel channel to the fuel manifold.