An indoor unit of an air-conditioning apparatus, comprising: a main body provided with an opening port; and a rectangular decorative panel attached to the main body to cover the opening port, the decorative panel including a rectangular suction grille provided to face the opening port of the main body, the suction grille having one side rotatably supported on one side of the decorative panel, and being detachably attached to the decorative panel, the one side of the suction grille and the one side of the decorative panel being secured to each other by a plurality of fall prevention strings each extending between the suction grille and the decorative panel, the decorative panel being provided with two panel claw portions to which respective portions of the plurality of fall prevention strings are to be hooked, the suction grille is provided with two grille claw portions to which respective end portions of the plurality of fall prevention strings are to be hooked, and the two panel claw portions and the two grille claw portions being arranged such that a distance W1 between the two panel claw portions is greater than a distance W2 between the two grille claw portions, the two panel claw portions are arranged in a longitudinal direction of the decorative panel, and the two grille claw portions are arranged in a longitudinal direction of the suction grille, and the distance W1 between the two panel claw portions and the distance W2 between the two grille claw portions are determined such that tension forces X by the fall prevention strings which act in the longitudinal direction of the suction grille are equivalent to tension forces Z by the fall prevention strings which act in a vertical direction. a main body provided with an opening port; and a rectangular decorative panel attached to the main body to cover the opening port, the decorative panel including a rectangular suction grille provided to face the opening port of the main body, the suction grille having one side rotatably supported on one side of the decorative panel, and being detachably attached to the decorative panel, the one side of the suction grille and the one side of the decorative panel being secured to each other by a plurality of fall prevention strings each extending between the suction grille and the decorative panel, the decorative panel being provided with two panel claw portions to which respective portions of the plurality of fall prevention strings are to be hooked, the suction grille is provided with two grille claw portions to which respective end portions of the plurality of fall prevention strings are to be hooked, and the two panel claw portions and the two grille claw portions being arranged such that a distance W1 between the two panel claw portions is greater than a distance W2 between the two grille claw portions, the two panel claw portions are arranged in a longitudinal direction of the decorative panel, and the two grille claw portions are arranged in a longitudinal direction of the suction grille, and the distance W1 between the two panel claw portions and the distance W2 between the two grille claw portions are determined such that tension forces X by the fall prevention strings which act in the longitudinal direction of the suction grille are equivalent to tension forces Z by the fall prevention strings which act in a vertical direction.