A linear compressor comprising: a shell to which a suction pipe is coupled; a cylinder disposed inside the shell to define a compression space; a piston reciprocating inside the cylinder to compress a refrigerant in the compression space; and a muffler coupled to the piston and having an inlet through which the refrigerant is introduced and an outlet through which the refrigerant is discharged, wherein the muffler includes a plurality of flow tubes (212, 222, 240) extending in a flow direction of the refrigerant from the inlet to the outlet, wherein the plurality of flow tubes (212, 222, 240) include at least one variable portion having a flow cross-sectional area widened in the flow direction, wherein the at least one variable portion is formed in any one of the plurality of flow tubes (212, 222, 240), wherein the muffler includes: a first muffler (210, 210a), at least a part of which is disposed inside the piston; a second muffler (220, 220a) coupled to a rear portion of the first muffler (210, 210a); and a third muffler (230, 230a) in which the second muffler (220, 220a) is accommodated and which is coupled to a rear portion of the piston, wherein the plurality of flow tubes includes a first flow tube (212, 212a) provided in the first muffler (210, 210a) and a second flow tube (222, 222a) provided in the second muffler (220, 220a), wherein the at least one variable portion is formed in the first flow tube, and wherein cross sections of outlets of the first flow tube are larger than cross sections of inlets of the first flow tube, characterized in that: an outer side and an inner side of the first flow tube have an inclined structure extending continuously from the inlet to the outlet. a shell to which a suction pipe is coupled; a cylinder disposed inside the shell to define a compression space; a piston reciprocating inside the cylinder to compress a refrigerant in the compression space; and a muffler coupled to the piston and having an inlet through which the refrigerant is introduced and an outlet through which the refrigerant is discharged, wherein the muffler includes a plurality of flow tubes (212, 222, 240) extending in a flow direction of the refrigerant from the inlet to the outlet, wherein the plurality of flow tubes (212, 222, 240) include at least one variable portion having a flow cross-sectional area widened in the flow direction, wherein the at least one variable portion is formed in any one of the plurality of flow tubes (212, 222, 240), wherein the muffler includes: a first muffler (210, 210a), at least a part of which is disposed inside the piston; a second muffler (220, 220a) coupled to a rear portion of the first muffler (210, 210a); and a third muffler (230, 230a) in which the second muffler (220, 220a) is accommodated and which is coupled to a rear portion of the piston, wherein the plurality of flow tubes includes a first flow tube (212, 212a) provided in the first muffler (210, 210a) and a second flow tube (222, 222a) provided in the second muffler (220, 220a), wherein the at least one variable portion is formed in the first flow tube, and wherein cross sections of outlets of the first flow tube are larger than cross sections of inlets of the first flow tube, characterized in that: an outer side and an inner side of the first flow tube have an inclined structure extending continuously from the inlet to the outlet. a first muffler (210, 210a), at least a part of which is disposed inside the piston; a second muffler (220, 220a) coupled to a rear portion of the first muffler (210, 210a); and a third muffler (230, 230a) in which the second muffler (220, 220a) is accommodated and which is coupled to a rear portion of the piston, wherein the plurality of flow tubes includes a first flow tube (212, 212a) provided in the first muffler (210, 210a) and a second flow tube (222, 222a) provided in the second muffler (220, 220a), wherein the at least one variable portion is formed in the first flow tube, and wherein cross sections of outlets of the first flow tube are larger than cross sections of inlets of the first flow tube, characterized in that: an outer side and an inner side of the first flow tube have an inclined structure extending continuously from the inlet to the outlet.