A burner for an exhaust purifying device includes a tube, an air supply port for supplying air for combustion into the tube, a fuel supply port for supplying fuel into the tube, and an ignition portion. The tube includes a premixing chamber for mixing air for combustion and fuel to generate a pre-mixed air-fuel mixture, a combustion chamber for combusting the pre-mixed air-fuel mixture to generate post-combustion gas, and a discharge port for discharging the post-combustion gas. The ignition portion ignites the pre-mixed air-fuel mixture in the combustion chamber. The tube further includes a swirling flow generation unit arranged upstream of the premixing chamber for generating a swirling flow of which the center direction corresponds to a fuel injection direction and a diffusion unit arranged downstream of the swirling flow generation unit in the premixing chamber for diffusing the fuel incorporated in the swirling flow.