A linear compressor, comprising: a shell comprising a suction inlet; a cylinder provided in the shell to define a compression space for a refrigerant; a piston reciprocated in an axial direction within the cylinder; a discharge valve provided at one end of the cylinder to selectively discharge the refrigerant compressed in the compression space; at least one nozzle disposed on the cylinder and through which at least a portion of the refrigerant discharged through the discharge valve flows; and at least one expansion portion (200, 400) that extends from the at least one nozzle to an inner circumferential surface of the cylinder, wherein the expansion portion (200, 400) has a cross-sectional area greater than a cross-sectional area of the at least one nozzle, the linear compressor further comprises: at least one gas inflow recessed from an outer circumferential surface of the cylinder; and a thread filter that is wound several times around the at least one gas inflow, wherein the at least one nozzle comprises a nozzle inlet connected to the gas inflow and a nozzle outlet connected to the expansion portion (200, 400), wherein the at least one expansion portion (200, 400) has a width in the axial direction and a height in a radial direction, and wherein the height of the at least one expansion portion (200, 400) in the radial direction is equal to or greater than a height of a space between the cylinder and the piston in the radial direction. a shell comprising a suction inlet; a cylinder provided in the shell to define a compression space for a refrigerant; a piston reciprocated in an axial direction within the cylinder; a discharge valve provided at one end of the cylinder to selectively discharge the refrigerant compressed in the compression space; at least one nozzle disposed on the cylinder and through which at least a portion of the refrigerant discharged through the discharge valve flows; and at least one expansion portion (200, 400) that extends from the at least one nozzle to an inner circumferential surface of the cylinder, wherein the expansion portion (200, 400) has a cross-sectional area greater than a cross-sectional area of the at least one nozzle, the linear compressor further comprises: at least one gas inflow recessed from an outer circumferential surface of the cylinder; and a thread filter that is wound several times around the at least one gas inflow, wherein the at least one nozzle comprises a nozzle inlet connected to the gas inflow and a nozzle outlet connected to the expansion portion (200, 400), wherein the at least one expansion portion (200, 400) has a width in the axial direction and a height in a radial direction, and wherein the height of the at least one expansion portion (200, 400) in the radial direction is equal to or greater than a height of a space between the cylinder and the piston in the radial direction. at least one gas inflow recessed from an outer circumferential surface of the cylinder; and a thread filter that is wound several times around the at least one gas inflow, wherein the at least one nozzle comprises a nozzle inlet connected to the gas inflow and a nozzle outlet connected to the expansion portion (200, 400), wherein the at least one expansion portion (200, 400) has a width in the axial direction and a height in a radial direction, and wherein the height of the at least one expansion portion (200, 400) in the radial direction is equal to or greater than a height of a space between the cylinder and the piston in the radial direction.