A laundry treating apparatus comprising: a drum having a mounting slot, the drum being configured to rotate about a rotation axis extending in a front-rear direction; and a lifter (61a, 62a, 63a, 61b, 62b, 63b) disposed on an inner circumferential surface of the drum and configured to revolve about the rotation axis when the drum rotates, wherein the lifter (61a, 62a, 63a, 61b, 62b, 63b) comprises: a lifter frame installed on the inner circumferential surface of the drum; and a frame cover coupled to the lifter frame and protruding radially inward from the inner circumferential surface of the drum, wherein the lifter frame comprises: a frame base coupled to the inner circumferential surface of the drum and formed in the form of a closed curve formed by a single line; a frame upper plate spaced apart from the frame base in a direction toward the inside of the drum and having a horizontal projection plane positioned in the closed curve of the frame base; an insertion protrusion configured to be inserted into the mounting slot, and comprising a vertical portion extending downward from a bottom surface of the frame base and a catching portion bent in a direction toward the inside of the closed curve at a lower end of the vertical portion, characterized by the lifter frame further comprising: a frame sidewall configured to connect the frame upper plate and the frame base and having a lateral throughhole formed by penetrating a part of the frame sidewall; and wherein a horizontal projection plane of the catching portion is positioned in a horizontal projection plane of the lateral throughhole. a drum having a mounting slot, the drum being configured to rotate about a rotation axis extending in a front-rear direction; and a lifter (61a, 62a, 63a, 61b, 62b, 63b) disposed on an inner circumferential surface of the drum and configured to revolve about the rotation axis when the drum rotates, wherein the lifter (61a, 62a, 63a, 61b, 62b, 63b) comprises: a lifter frame installed on the inner circumferential surface of the drum; and a frame cover coupled to the lifter frame and protruding radially inward from the inner circumferential surface of the drum, wherein the lifter frame comprises: a frame base coupled to the inner circumferential surface of the drum and formed in the form of a closed curve formed by a single line; a frame upper plate spaced apart from the frame base in a direction toward the inside of the drum and having a horizontal projection plane positioned in the closed curve of the frame base; an insertion protrusion configured to be inserted into the mounting slot, and comprising a vertical portion extending downward from a bottom surface of the frame base and a catching portion bent in a direction toward the inside of the closed curve at a lower end of the vertical portion, characterized by the lifter frame further comprising: a frame sidewall configured to connect the frame upper plate and the frame base and having a lateral throughhole formed by penetrating a part of the frame sidewall; and wherein a horizontal projection plane of the catching portion is positioned in a horizontal projection plane of the lateral throughhole. a lifter frame installed on the inner circumferential surface of the drum; and a frame cover coupled to the lifter frame and protruding radially inward from the inner circumferential surface of the drum, wherein the lifter frame comprises: a frame base coupled to the inner circumferential surface of the drum and formed in the form of a closed curve formed by a single line; a frame upper plate spaced apart from the frame base in a direction toward the inside of the drum and having a horizontal projection plane positioned in the closed curve of the frame base; an insertion protrusion configured to be inserted into the mounting slot, and comprising a vertical portion extending downward from a bottom surface of the frame base and a catching portion bent in a direction toward the inside of the closed curve at a lower end of the vertical portion, characterized by the lifter frame further comprising: a frame sidewall configured to connect the frame upper plate and the frame base and having a lateral throughhole formed by penetrating a part of the frame sidewall; and wherein a horizontal projection plane of the catching portion is positioned in a horizontal projection plane of the lateral throughhole. a frame base coupled to the inner circumferential surface of the drum and formed in the form of a closed curve formed by a single line; a frame upper plate spaced apart from the frame base in a direction toward the inside of the drum and having a horizontal projection plane positioned in the closed curve of the frame base; an insertion protrusion configured to be inserted into the mounting slot, and comprising a vertical portion extending downward from a bottom surface of the frame base and a catching portion bent in a direction toward the inside of the closed curve at a lower end of the vertical portion, characterized by the lifter frame further comprising: a frame sidewall configured to connect the frame upper plate and the frame base and having a lateral throughhole formed by penetrating a part of the frame sidewall; and wherein a horizontal projection plane of the catching portion is positioned in a horizontal projection plane of the lateral throughhole. a frame sidewall configured to connect the frame upper plate and the frame base and having a lateral throughhole formed by penetrating a part of the frame sidewall; and wherein a horizontal projection plane of the catching portion is positioned in a horizontal projection plane of the lateral throughhole.