An indoor unit of an air conditioner comprising: a housing; a blowing fan and a heat exchanger accommodated in the housing; a blowout port extending in a horizontal direction and provided in a lower portion of the housing to blow air from the blowing fan into a room; a fixing portion provided to cross the blowout port; a groove portion provided in the fixing portion to be recessed from an end portion on a downstream side of the air flow toward an upstream side; a protective member which is disposed on the downstream side of the fixing portion, covers the blowout port allowing ventilation, and has a plurality of rod-like horizontal rails having elasticity, extending in the horizontal direction and disposed to be spaced apart from each other in a vertical direction intersecting with the horizontal direction,and capable of being inserted into the groove portion; and a locking member which is locked to the fixing portion from the downstream side of the protective member to restrict movement of the rail inserted into the groove portion; the indoor unit being characterized in that the protective member further has a rod-like vertical rail which is disposed to extend in the vertical direction at a position of a louver provided at the blowout port so as to extend in the vertical direction, and connects and fixes the plurality of horizontal rails, in that the groove portion includes a narrowing portion having a pair of inclined guide surfaces in which a width gradually decreases from the downstream side toward the upstream side, and an expanded accommodating portion provided to be wider than the narrowing portion on the upstream side of the narrowing portion and capable of locking and accommodating the rod-like horizontal rails, wherein the width of the expanded accommodating portion in the vertical direction equals the sum of the widths of two adjacent horizontal rails accommodated in the expanded accommodating portion and the interval between them, wherein the expanded accommodating portion is provided to be continuous with the narrowing portion and to expand the groove width on both sides in the vertical direction. a housing; a blowing fan and a heat exchanger accommodated in the housing; a blowout port extending in a horizontal direction and provided in a lower portion of the housing to blow air from the blowing fan into a room; a fixing portion provided to cross the blowout port; a groove portion provided in the fixing portion to be recessed from an end portion on a downstream side of the air flow toward an upstream side; a protective member which is disposed on the downstream side of the fixing portion, covers the blowout port allowing ventilation, and has a plurality of rod-like horizontal rails having elasticity, extending in the horizontal direction and disposed to be spaced apart from each other in a vertical direction intersecting with the horizontal direction,and capable of being inserted into the groove portion; and a locking member which is locked to the fixing portion from the downstream side of the protective member to restrict movement of the rail inserted into the groove portion; the indoor unit being characterized in that the protective member further has a rod-like vertical rail which is disposed to extend in the vertical direction at a position of a louver provided at the blowout port so as to extend in the vertical direction, and connects and fixes the plurality of horizontal rails, in that the groove portion includes a narrowing portion having a pair of inclined guide surfaces in which a width gradually decreases from the downstream side toward the upstream side, and an expanded accommodating portion provided to be wider than the narrowing portion on the upstream side of the narrowing portion and capable of locking and accommodating the rod-like horizontal rails, wherein the width of the expanded accommodating portion in the vertical direction equals the sum of the widths of two adjacent horizontal rails accommodated in the expanded accommodating portion and the interval between them, wherein the expanded accommodating portion is provided to be continuous with the narrowing portion and to expand the groove width on both sides in the vertical direction.