Provided is an axial flow turbine that can enhance an effect of reducing a mixing loss. The axial flow turbine includes: a plurality of stator blades 2 provided on the inner circumferential side of a diaphragm outer ring 1; a plurality of rotor blades 5 provided on the outer circumferential side of a rotor 4; a shroud 6 provided on the outer circumferential side of the plurality of rotor blades 5; an annular groove portion 12 formed in the diaphragm outer ring 1 and housing the shroud 6 therein; a clearance passage 13 defined between the groove portion 12 of the diaphragm outer ring 1 and the shroud 6, into which a portion of working fluid flows from the downstream side of the stator blades 2 in a main passage 7; the clearance passage 13 from which the portion of the working fluid flows out toward the downstream side of the rotor blades 5 in the main passage 7; seal fins (14A to 14D) provided in the clearance passage 13; a circulation flow generating chamber 17 defined on the downstream side of the clearance passage 13; and a plurality of shielding plates 18 secured to the diaphragm outer ring 1 in such a manner as to be located in the circulation flow generating chamber 17, the shielding plates 18 extending in the axial and radial directions of the rotor.
