A cleaner comprising: a body having an intake port configured to take in air and an outtake port configured to discharge air; a dust-separating apparatus detachably mounted on the body and configured to centrifugate dirt from the air taken in; and a fan motor assembly configured to form an intake force used to take in the air, wherein the dust-separating apparatus comprises: an outer case forming an external appearance of the dust-separating apparatus; an inner case coupled to a rear surface of the outer case while having one portion disposed inside the outer case; a rear case coupled to a rear surface of the inner case; and a cover disposed at an opposite side of the inner case with respect to the outer case; wherein the outer case comprises: a guide passage configured to guide air introduced through the dust-separating apparatus inlet to a rear side; a first cyclone part configured to firstly perform a centrifugation separation on dirt while guiding the air passing through the guide passage to a front side and; a first dust-collecting compartment configured to collect the dirt separated by the first cyclone part; a first purified air exhaust pipe configured to guide the air passing through the first cyclone part to the rear side again; and wherein the inner case comprises: a plurality of second cyclone pipes each with a second cyclone part disposed inside the outer case and configured to secondarily perform a centrifugal separation on dirt while guiding the air passing through the first purified air exhaust pipe to the front side; a second dust-collecting compartment configured to collect dirt separated by the second cyclone part, which is provided with at least one second cyclone part, a second purified air exhaust pipe configured to guide air passing through the second cyclone part to the rear side again; and a dust separating apparatus outlet connected to the outtake port to exhaust air passing through the second purified air exhaust pipe, wherein the cover comprises an air inlet connected to the intake port. a body having an intake port configured to take in air and an outtake port configured to discharge air; a dust-separating apparatus detachably mounted on the body and configured to centrifugate dirt from the air taken in; and a fan motor assembly configured to form an intake force used to take in the air, wherein the dust-separating apparatus comprises: an outer case forming an external appearance of the dust-separating apparatus; an inner case coupled to a rear surface of the outer case while having one portion disposed inside the outer case; a rear case coupled to a rear surface of the inner case; and a cover disposed at an opposite side of the inner case with respect to the outer case; an outer case forming an external appearance of the dust-separating apparatus; an inner case coupled to a rear surface of the outer case while having one portion disposed inside the outer case; a rear case coupled to a rear surface of the inner case; and a cover disposed at an opposite side of the inner case with respect to the outer case; wherein the outer case comprises: a guide passage configured to guide air introduced through the dust-separating apparatus inlet to a rear side; a first cyclone part configured to firstly perform a centrifugation separation on dirt while guiding the air passing through the guide passage to a front side and; a first dust-collecting compartment configured to collect the dirt separated by the first cyclone part; a guide passage configured to guide air introduced through the dust-separating apparatus inlet to a rear side; a first cyclone part configured to firstly perform a centrifugation separation on dirt while guiding the air passing through the guide passage to a front side and; a first dust-collecting compartment configured to collect the dirt separated by the first cyclone part; a first purified air exhaust pipe configured to guide the air passing through the first cyclone part to the rear side again; and wherein the inner case comprises: a plurality of second cyclone pipes each with a second cyclone part disposed inside the outer case and configured to secondarily perform a centrifugal separation on dirt while guiding the air passing through the first purified air exhaust pipe to the front side; a second dust-collecting compartment configured to collect dirt separated by the second cyclone part, which is provided with at least one second cyclone part, a second purified air exhaust pipe configured to guide air passing through the second cyclone part to the rear side again; and a dust separating apparatus outlet connected to the outtake port to exhaust air passing through the second purified air exhaust pipe, wherein the cover comprises an air inlet connected to the intake port. a plurality of second cyclone pipes each with a second cyclone part disposed inside the outer case and configured to secondarily perform a centrifugal separation on dirt while guiding the air passing through the first purified air exhaust pipe to the front side; a second dust-collecting compartment configured to collect dirt separated by the second cyclone part, which is provided with at least one second cyclone part, a second purified air exhaust pipe configured to guide air passing through the second cyclone part to the rear side again; and a dust separating apparatus outlet connected to the outtake port to exhaust air passing through the second purified air exhaust pipe, wherein the cover comprises an air inlet connected to the intake port.