A robot cleaner comprising: a cleaner main body equipped with a dust collecting device; a cleaning module that is relatively movable with respect to the cleaner main body and sucks air containing dust and foreign substances; and a connection unit that is connected to the cleaner main body and the cleaning module respectively and has a variable length, wherein the connection unit forms a part of an intake flow path that guides the air sucked by the cleaning module to the dust collecting device, wherein the connection unit comprises: an outer case mounted on the cleaner main body, an inner case that is inserted into the outer case and relatively moveable with respect to the outer case, and a flexible tube which is fixed to the outer case and the inner case, respectively, and of which at least a part is provided to extend or contract according to the relative movement of the inner case, characterized in that a hole connecting with inside of the outer case is provided on an outer circumference of the outer case, and wherein the flexible tube comprises a corrugated portion including a ductile material and provided to extend or contract according to the relative movement of the inner case, and a bending portion extending from the corrugated portion and penetrating the hole. a cleaner main body equipped with a dust collecting device; a cleaning module that is relatively movable with respect to the cleaner main body and sucks air containing dust and foreign substances; and a connection unit that is connected to the cleaner main body and the cleaning module respectively and has a variable length, wherein the connection unit forms a part of an intake flow path that guides the air sucked by the cleaning module to the dust collecting device, wherein the connection unit comprises: an outer case mounted on the cleaner main body, an inner case that is inserted into the outer case and relatively moveable with respect to the outer case, and a flexible tube which is fixed to the outer case and the inner case, respectively, and of which at least a part is provided to extend or contract according to the relative movement of the inner case, characterized in that a hole connecting with inside of the outer case is provided on an outer circumference of the outer case, and wherein the flexible tube comprises a corrugated portion including a ductile material and provided to extend or contract according to the relative movement of the inner case, and a bending portion extending from the corrugated portion and penetrating the hole. an outer case mounted on the cleaner main body, an inner case that is inserted into the outer case and relatively moveable with respect to the outer case, and a flexible tube which is fixed to the outer case and the inner case, respectively, and of which at least a part is provided to extend or contract according to the relative movement of the inner case, characterized in that a hole connecting with inside of the outer case is provided on an outer circumference of the outer case, and wherein the flexible tube comprises a corrugated portion including a ductile material and provided to extend or contract according to the relative movement of the inner case, and a bending portion extending from the corrugated portion and penetrating the hole.