A piston for an internal combustion engine, the piston comprising: a body comprising a piston pin boss for inserting a piston pin thereinto, and a skirt corresponding to a cylinder wall; and a cooling channel provided in the body to allow a refrigerant for cooling the body, to flow therethrough, and having a ring shape comprising a first channel provided from a refrigerant inlet to a refrigerant outlet along a first outer circumferential direction of the body, and a second channel provided from the refrigerant inlet to the refrigerant outlet along a second outer circumferential direction of the body, wherein, in the cooling channel, to increase a supply speed and a discharge speed of the refrigerant by inducing the refrigerant supplied through the refrigerant inlet, toward the refrigerant outlet, a first space cross-sectional area of a first part of the first channel located relatively close to the refrigerant inlet is less than a second space cross-sectional area of a second part of the first channel located relatively far from the refrigerant inlet, and a third space cross-sectional area of a third part of the second channel located relatively close to the refrigerant inlet is less than a fourth space cross-sectional area of a fourth part of the second channel located relatively far from the refrigerant inlet, wherein the cooling channel has a shape in which an upper surface height is equal and a lower surface height is also equal at every part, and an upper part width of a space cross-section of the second part is greater than an upper part width of a space cross-section of the first part; and characterised in that the cross-section of the first part has a relatively small upper part width and a relatively large lower part width. a body comprising a piston pin boss for inserting a piston pin thereinto, and a skirt corresponding to a cylinder wall; and a cooling channel provided in the body to allow a refrigerant for cooling the body, to flow therethrough, and having a ring shape comprising a first channel provided from a refrigerant inlet to a refrigerant outlet along a first outer circumferential direction of the body, and a second channel provided from the refrigerant inlet to the refrigerant outlet along a second outer circumferential direction of the body, wherein, in the cooling channel, to increase a supply speed and a discharge speed of the refrigerant by inducing the refrigerant supplied through the refrigerant inlet, toward the refrigerant outlet, a first space cross-sectional area of a first part of the first channel located relatively close to the refrigerant inlet is less than a second space cross-sectional area of a second part of the first channel located relatively far from the refrigerant inlet, and a third space cross-sectional area of a third part of the second channel located relatively close to the refrigerant inlet is less than a fourth space cross-sectional area of a fourth part of the second channel located relatively far from the refrigerant inlet, wherein the cooling channel has a shape in which an upper surface height is equal and a lower surface height is also equal at every part, and an upper part width of a space cross-section of the second part is greater than an upper part width of a space cross-section of the first part; and characterised in that the cross-section of the first part has a relatively small upper part width and a relatively large lower part width.