A robot cleaner, comprising: a motor assembly, wherein the motor assembly comprises: a fan motor for suctioning air through a fan intake port provided at the front surface thereof and discharging the air through a discharge port formed at the rear surface thereof, wherein the fan motor includes a printed circuit board that is spaced apart from a rear surface of the fan motor and an extension part which covers a portion of a space between the printed circuit board and the rear surface of the fan motor; and a fan motor casing encasing the fan motor, and including an exhaust passage for guiding, to an exhaust port, the air discharged from the fan motor, wherein the exhaust passage of the fan motor casing includes: a first exhaust passage formed at the rear surface of the fan motor, and guiding the air such that the air, discharged from the discharge port of the fan motor, moves to an upper or lower side of the fan motor; a second exhaust passage formed at the upper or lower side of the fan motor, and guiding, to a front end of the fan motor, the air discharged from the first exhaust passage; a third exhaust passage (C-1, C-2) provided at a left and right sides of the fan motor, and guiding the air such that the air, discharged from the second exhaust passage, moves to the lower or upper side of the fan motor along the left and right sides of the fan motor; and a fourth exhaust passage provided at the lower or upper side of the fan motor, and guiding, to the exhaust port, the air having moved along the left and right sides of the third exhaust passage (C-1, C-2), and wherein the first exhaust passage is formed by the printed circuit board and the extension part. a motor assembly, wherein the motor assembly comprises: a fan motor for suctioning air through a fan intake port provided at the front surface thereof and discharging the air through a discharge port formed at the rear surface thereof, wherein the fan motor includes a printed circuit board that is spaced apart from a rear surface of the fan motor and an extension part which covers a portion of a space between the printed circuit board and the rear surface of the fan motor; and a fan motor casing encasing the fan motor, and including an exhaust passage for guiding, to an exhaust port, the air discharged from the fan motor, a fan motor for suctioning air through a fan intake port provided at the front surface thereof and discharging the air through a discharge port formed at the rear surface thereof, wherein the fan motor includes a printed circuit board that is spaced apart from a rear surface of the fan motor and an extension part which covers a portion of a space between the printed circuit board and the rear surface of the fan motor; and a fan motor casing encasing the fan motor, and including an exhaust passage for guiding, to an exhaust port, the air discharged from the fan motor, wherein the exhaust passage of the fan motor casing includes: a first exhaust passage formed at the rear surface of the fan motor, and guiding the air such that the air, discharged from the discharge port of the fan motor, moves to an upper or lower side of the fan motor; a second exhaust passage formed at the upper or lower side of the fan motor, and guiding, to a front end of the fan motor, the air discharged from the first exhaust passage; a third exhaust passage (C-1, C-2) provided at a left and right sides of the fan motor, and guiding the air such that the air, discharged from the second exhaust passage, moves to the lower or upper side of the fan motor along the left and right sides of the fan motor; and a fourth exhaust passage provided at the lower or upper side of the fan motor, and guiding, to the exhaust port, the air having moved along the left and right sides of the third exhaust passage (C-1, C-2), and a first exhaust passage formed at the rear surface of the fan motor, and guiding the air such that the air, discharged from the discharge port of the fan motor, moves to an upper or lower side of the fan motor; a second exhaust passage formed at the upper or lower side of the fan motor, and guiding, to a front end of the fan motor, the air discharged from the first exhaust passage; a third exhaust passage (C-1, C-2) provided at a left and right sides of the fan motor, and guiding the air such that the air, discharged from the second exhaust passage, moves to the lower or upper side of the fan motor along the left and right sides of the fan motor; and a fourth exhaust passage provided at the lower or upper side of the fan motor, and guiding, to the exhaust port, the air having moved along the left and right sides of the third exhaust passage (C-1, C-2), and wherein the first exhaust passage is formed by the printed circuit board and the extension part.