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).