A two-stroke engine that executes scavenging by supplying fresh gas pre-compressed in a crank chamber through scavenging ports to a combustion chamber in a scavenging process, comprising: at least four scavenging ports , the four scavenging ports including: first right (34 rig-1) and left (34 lef-1) scavenging ports that lie on a side relatively away from an exhaust port and that lie facing each other with a cylinder in between; and second right (34 rig-2) and left (34 lef-2) scavenging ports that lie closer to the exhaust port than the first right and left scavenging ports (34 rig-1, 34 lef-1) do and that lie facing each other with the cylinder in between, characterized in that the second left scavenging port (34 lef-2) and the first right scavenging port (34 rig-1) that make up a first mutually diagonal set (Diag-No. 1) have different opening timings from those of the first left scavenging port (34 lef-1) and the second right scavenging port (34 rig-2) that make up a second mutually diagonal set (Diag-No. 2), wherein each of the four scavenging ports has an upper edge , the upper edge defining the opening timing of the scavenging port , and the upper edges of the two scavenging ports (34 lef-2, 34 rig-1) making up the first set (Diag-No. 1) have height levels different from those of the upper edges of the two scavenging ports (34 lef-1, 34 rig-2) making up the second set (Diag-No. 2). at least four scavenging ports , the four scavenging ports including: first right (34 rig-1) and left (34 lef-1) scavenging ports that lie on a side relatively away from an exhaust port and that lie facing each other with a cylinder in between; and second right (34 rig-2) and left (34 lef-2) scavenging ports that lie closer to the exhaust port than the first right and left scavenging ports (34 rig-1, 34 lef-1) do and that lie facing each other with the cylinder in between, characterized in that the second left scavenging port (34 lef-2) and the first right scavenging port (34 rig-1) that make up a first mutually diagonal set (Diag-No. 1) have different opening timings from those of the first left scavenging port (34 lef-1) and the second right scavenging port (34 rig-2) that make up a second mutually diagonal set (Diag-No. 2), wherein each of the four scavenging ports has an upper edge , the upper edge defining the opening timing of the scavenging port , and the upper edges of the two scavenging ports (34 lef-2, 34 rig-1) making up the first set (Diag-No. 1) have height levels different from those of the upper edges of the two scavenging ports (34 lef-1, 34 rig-2) making up the second set (Diag-No. 2). first right (34 rig-1) and left (34 lef-1) scavenging ports that lie on a side relatively away from an exhaust port and that lie facing each other with a cylinder in between; and second right (34 rig-2) and left (34 lef-2) scavenging ports that lie closer to the exhaust port than the first right and left scavenging ports (34 rig-1, 34 lef-1) do and that lie facing each other with the cylinder in between, characterized in that the second left scavenging port (34 lef-2) and the first right scavenging port (34 rig-1) that make up a first mutually diagonal set (Diag-No. 1) have different opening timings from those of the first left scavenging port (34 lef-1) and the second right scavenging port (34 rig-2) that make up a second mutually diagonal set (Diag-No. 2), wherein each of the four scavenging ports has an upper edge , the upper edge defining the opening timing of the scavenging port , and the upper edges of the two scavenging ports (34 lef-2, 34 rig-1) making up the first set (Diag-No. 1) have height levels different from those of the upper edges of the two scavenging ports (34 lef-1, 34 rig-2) making up the second set (Diag-No. 2). <EOS>