A uniflow scavenging two-cycle engine comprising: a cylinder inside which a combustion chamber is formed; a piston which slides within the cylinder; a scavenge port which is provided on a lower side in a vertical direction being a stroke direction of the piston in the cylinder, and sucks an active gas into the combustion chamber in accordance with the sliding movement of the piston; characterized in that a fuel injection unit (126, 226, 326) which includes: a mixing tube (126a, 226a, 326a, 126b, 226b, 325b) which surrounds the cylinder at a radially outer side thereof in a circumferential direction; and a circulation tube (126e, 226e, 326e, 126f, 226f, 326f) which communicates with the mixing tube (126a, 226a, 326a, 126b, 226b, 325b); and wherein a plurality of injection units (126g, 226g, 326g, 126h, 226h, 326h) which include openings which inject a fuel gas into the active gas sucked into the scavenge port are provided at different positions in the vertical direction on the circulation tube (126e, 226e, 326e, 126f, 226f, 326f), the plurality of injection units (126g, 226g, 326g, 126h, 226h, 326h) are divided into at least two sets of injection unit groups include a first injection unit group and a second injection unit group, the first injection unit group being a set of one or a plurality of injection units (126g, 226g, 326g), the second injection unit group being a set of one or a plurality of injection units (126h, 226h, 326h) located on the lower side from the first injection unit group in the vertical direction, and the injection stop of the fuel gas is later in the injection unit (126g, 226g, 326g) of the first injection unit group than in the injection unit (126h, 226h, 432) of the second injection unit group. a cylinder inside which a combustion chamber is formed; a piston which slides within the cylinder; a scavenge port which is provided on a lower side in a vertical direction being a stroke direction of the piston in the cylinder, and sucks an active gas into the combustion chamber in accordance with the sliding movement of the piston; characterized in that a fuel injection unit (126, 226, 326) which includes: a mixing tube (126a, 226a, 326a, 126b, 226b, 325b) which surrounds the cylinder at a radially outer side thereof in a circumferential direction; and a circulation tube (126e, 226e, 326e, 126f, 226f, 326f) which communicates with the mixing tube (126a, 226a, 326a, 126b, 226b, 325b); and wherein a plurality of injection units (126g, 226g, 326g, 126h, 226h, 326h) which include openings which inject a fuel gas into the active gas sucked into the scavenge port are provided at different positions in the vertical direction on the circulation tube (126e, 226e, 326e, 126f, 226f, 326f), the plurality of injection units (126g, 226g, 326g, 126h, 226h, 326h) are divided into at least two sets of injection unit groups include a first injection unit group and a second injection unit group, the first injection unit group being a set of one or a plurality of injection units (126g, 226g, 326g), the second injection unit group being a set of one or a plurality of injection units (126h, 226h, 326h) located on the lower side from the first injection unit group in the vertical direction, and the injection stop of the fuel gas is later in the injection unit (126g, 226g, 326g) of the first injection unit group than in the injection unit (126h, 226h, 432) of the second injection unit group.