A robot cleaner comprising: a main body; a traveling unit installed in the main body and moving the main body; an ultrasonic sensor emitting an oscillation wave for a predetermined period of time ta, receiving a reflection wave reflected from an object, and outputting vibration generated by the oscillation wave and vibration generated by the reception of the reflection wave as an electrical signal; and a controller determining information about the object surface based on the electrical signal output from the ultrasonic sensor, and controlling movement of the traveling unit based on the information about the object surface, wherein the electrical signal includes an electrical signal for a first composite wave appearing for a predetermined period of time ta when the oscillation wave overlaps the reflection wave, and after the predetermined time period ta has elapsed an electrical signal for a second composite wave appearing when the ultrasonic sensor is subject to an aftershock by inertia with a gradually decaying amplitude overlapping the reflection wave, wherein the controller calculates an average amplitude of the electrical signal based on amplitudes of the electrical signal of one of the first composite wave and the second composite wave, and calculates a tail length, which is a time of a signal having a value smaller than the average amplitude of the electrical signal, and determines the information about the object surface based on the tail length, and/or wherein the controller calculates an average deviation of the electrical signal of one of the first composite wave and the second composite wave using the average amplitude, and determines the information about the object surface using the calculated average deviation. a main body; a traveling unit installed in the main body and moving the main body; an ultrasonic sensor emitting an oscillation wave for a predetermined period of time ta, receiving a reflection wave reflected from an object, and outputting vibration generated by the oscillation wave and vibration generated by the reception of the reflection wave as an electrical signal; and a controller determining information about the object surface based on the electrical signal output from the ultrasonic sensor, and controlling movement of the traveling unit based on the information about the object surface, wherein the electrical signal includes an electrical signal for a first composite wave appearing for a predetermined period of time ta when the oscillation wave overlaps the reflection wave, and after the predetermined time period ta has elapsed an electrical signal for a second composite wave appearing when the ultrasonic sensor is subject to an aftershock by inertia with a gradually decaying amplitude overlapping the reflection wave, wherein the controller calculates an average amplitude of the electrical signal based on amplitudes of the electrical signal of one of the first composite wave and the second composite wave, and calculates a tail length, which is a time of a signal having a value smaller than the average amplitude of the electrical signal, and determines the information about the object surface based on the tail length, and/or wherein the controller calculates an average deviation of the electrical signal of one of the first composite wave and the second composite wave using the average amplitude, and determines the information about the object surface using the calculated average deviation.