An air conditioner comprising: an inlet through which indoor air is sucked; a heat exchanger that exchanges heat with said sucked indoor air; a blow-out port through which said heat-exchanged indoor air is blown out into a room; a blower having an impeller, being disposed on the downstream side of said heat exchanger between said inlet and said blow-out port with a longitudinal direction of an air conditioner main body serving as the rotary shaft direction thereof, and being rotated and driven by a motor and feeds said indoor air from said inlet to said blow-out port; a stabilizer that separates a suction-side channel on the upstream side of said impeller and a blow-out-side channel on the downstream side from each other and configures a front face side of said blow-out-side channel from said impeller to said blow-out port; a spiral guide wall that configures a rear face side of said blow-out-side channel from said impeller to said blow-out port; and a stepped portion disposed at least in a part of said guide wall and having a plurality of steps provided in parallel, each having an indented triangular shape in a section perpendicular to the rotary shaft of said impeller and extending in said rotary shaft direction, and forming steps in said direction in which said blower feeds the air, wherein in a section perpendicular to the rotary shaft of said impeller, an upstream-side end portion of one step of said stepped portion is made to be a step start portion, a portion indented the deepest in a triangular shape of said step is made to be a step deepest portion, a downstream-side end portion of said step is made to be a step end portion, and said step is configured such that a relationship among a length C1 connecting a rotation center O of said impeller to said step start portion, a length C2 connecting the rotation center O of said impeller to said step deepest portion, and a length C3 connecting the rotation center O of said impeller to said step end portion is C1 < C2 ≤ C3. an inlet through which indoor air is sucked; a heat exchanger that exchanges heat with said sucked indoor air; a blow-out port through which said heat-exchanged indoor air is blown out into a room; a blower having an impeller, being disposed on the downstream side of said heat exchanger between said inlet and said blow-out port with a longitudinal direction of an air conditioner main body serving as the rotary shaft direction thereof, and being rotated and driven by a motor and feeds said indoor air from said inlet to said blow-out port; a stabilizer that separates a suction-side channel on the upstream side of said impeller and a blow-out-side channel on the downstream side from each other and configures a front face side of said blow-out-side channel from said impeller to said blow-out port; a spiral guide wall that configures a rear face side of said blow-out-side channel from said impeller to said blow-out port; and a stepped portion disposed at least in a part of said guide wall and having a plurality of steps provided in parallel, each having an indented triangular shape in a section perpendicular to the rotary shaft of said impeller and extending in said rotary shaft direction, and forming steps in said direction in which said blower feeds the air, wherein in a section perpendicular to the rotary shaft of said impeller, an upstream-side end portion of one step of said stepped portion is made to be a step start portion, a portion indented the deepest in a triangular shape of said step is made to be a step deepest portion, a downstream-side end portion of said step is made to be a step end portion, and said step is configured such that a relationship among a length C1 connecting a rotation center O of said impeller to said step start portion, a length C2 connecting the rotation center O of said impeller to said step deepest portion, and a length C3 connecting the rotation center O of said impeller to said step end portion is C1 < C2 ≤ C3.