A linear compressor comprising: a shell ; a frame which is disposed within the shell and includes a frame head and a frame body extending in a longitudinal direction of the shell from a rear surface of the frame head ; a cylinder which is inserted into the frame body to form a portion of a compression space (P); a piston which is installed inside the cylinder so as to reciprocate therein; a motor assembly to move the piston in the axial direction of the cylinder to compress refrigerant suctioned into the compression space (P); a discharge cover unit which is coupled to one side of the frame and defines a discharge space in which refrigerant discharged from the compression space (P) is accommodated; and a valve spring assembly which is inserted into the discharge cover unit , includes a discharge valve , and provides an elastic force to the discharge valve in a direction in which the discharge valve is in contact with the cylinder , wherein the discharge cover unit includes a cover housing which is fixed to a front surface of the frame head and forms the discharge space having an opened surface, a discharge cover which is inserted to be in contact with an inner circumferential surface of the cover housing to cover the opened surface of the cover housing , characterised by a fixing ring which is provided on an inner circumferential surface of the discharge cover , and wherein the fixing ring is made of a material having a thermal expansion coefficient larger than that of the discharge cover . a shell ; a frame which is disposed within the shell and includes a frame head and a frame body extending in a longitudinal direction of the shell from a rear surface of the frame head ; a cylinder which is inserted into the frame body to form a portion of a compression space (P); a piston which is installed inside the cylinder so as to reciprocate therein; a motor assembly to move the piston in the axial direction of the cylinder to compress refrigerant suctioned into the compression space (P); a discharge cover unit which is coupled to one side of the frame and defines a discharge space in which refrigerant discharged from the compression space (P) is accommodated; and a valve spring assembly which is inserted into the discharge cover unit , includes a discharge valve , and provides an elastic force to the discharge valve in a direction in which the discharge valve is in contact with the cylinder , wherein the discharge cover unit includes a cover housing which is fixed to a front surface of the frame head and forms the discharge space having an opened surface, a discharge cover which is inserted to be in contact with an inner circumferential surface of the cover housing to cover the opened surface of the cover housing , characterised by a fixing ring which is provided on an inner circumferential surface of the discharge cover , and a cover housing which is fixed to a front surface of the frame head and forms the discharge space having an opened surface, a discharge cover which is inserted to be in contact with an inner circumferential surface of the cover housing to cover the opened surface of the cover housing , characterised by a fixing ring which is provided on an inner circumferential surface of the discharge cover , and wherein the fixing ring is made of a material having a thermal expansion coefficient larger than that of the discharge cover . <EOS>