An apparatus for changing capacity of scroll compressor comprises: a seal member movably installed on one of facing surfaces of a fixed scroll so as to seal a compression space made by the fixed scroll and orbiting scroll; a back pressure passage formed to be communicated from a point, where the seal member is contacted, to an outer circumferential surface of fixed scroll; an exhaust pipe installed on outer circumferential surface of the fixed scroll to be communicated with back pressure passage; and an exhaust pipe opening/closing valve installed on center part of exhaust pipe to open/close the exhaust pipe selectively, and thereby, sealability can be improved and low capacity can be outputted without decelerating orbiting scroll in low capacity operation.