A uniflow scavenging 2-cycle engine comprising: a cylinder in which a piston slides therein; a plurality of injection ports (132e, 232e) provided apart from each other in a circumferential direction of the cylinder; a fuel supply path configured to connect the plurality of injection ports (132e, 232e) to a fuel supply source of a fuel gas; a plurality of injection valves provided at the fuel supply path in parallel to each other, and which are configured to switch a communicating position at which the fuel supply source and the injection ports (132e, 232e) communicate with each other and the fuel gas supplied from the fuel supply source is ejected from the injection ports (132e, 232e) and a blocking position at which the communication between the fuel supply source and the injection ports (132e, 232e) is blocked and the ejection of the fuel gas from the injection ports (132e, 232e) is stopped, and thereby control the ejection of the fuel gas from the injection ports (132e, 232e); a hydraulic pump configured to discharge hydraulic oil and thereby switches the injection valves to the communicating position or the blocking position; a main flow path connected to the hydraulic pump and configured to guide the hydraulic oil discharged from the hydraulic pump; a plurality of branch flow paths which branch off from the main flow path and configured to guide the hydraulic oil to one or more of the injection valves from the main flow path; and switching valves provided at the plurality of respective branch flow paths, configured to supply the hydraulic oil from the main flow path to the injection valves or to stop the supply of the hydraulic oil from the main flow path to the injection valves, and configured to switch the injection valves to the communicating position or the blocking position, characterized in that at least one of the plurality of branch flow paths is connected to one or more of the injection valves that control the ejection of the fuel gas from the plurality of injection ports (132e, 232e) adjacent to each other in a circumferential direction of the cylinder, and the ejection of the fuel gas from the plurality of injection ports (132e, 232e) adjacent to each other is controlled by switching one switching valve provided at one of the branch flow paths. a cylinder in which a piston slides therein; a plurality of injection ports (132e, 232e) provided apart from each other in a circumferential direction of the cylinder; a fuel supply path configured to connect the plurality of injection ports (132e, 232e) to a fuel supply source of a fuel gas; a plurality of injection valves provided at the fuel supply path in parallel to each other, and which are configured to switch a communicating position at which the fuel supply source and the injection ports (132e, 232e) communicate with each other and the fuel gas supplied from the fuel supply source is ejected from the injection ports (132e, 232e) and a blocking position at which the communication between the fuel supply source and the injection ports (132e, 232e) is blocked and the ejection of the fuel gas from the injection ports (132e, 232e) is stopped, and thereby control the ejection of the fuel gas from the injection ports (132e, 232e); a hydraulic pump configured to discharge hydraulic oil and thereby switches the injection valves to the communicating position or the blocking position; a main flow path connected to the hydraulic pump and configured to guide the hydraulic oil discharged from the hydraulic pump; a plurality of branch flow paths which branch off from the main flow path and configured to guide the hydraulic oil to one or more of the injection valves from the main flow path; and switching valves provided at the plurality of respective branch flow paths, configured to supply the hydraulic oil from the main flow path to the injection valves or to stop the supply of the hydraulic oil from the main flow path to the injection valves, and configured to switch the injection valves to the communicating position or the blocking position, characterized in that at least one of the plurality of branch flow paths is connected to one or more of the injection valves that control the ejection of the fuel gas from the plurality of injection ports (132e, 232e) adjacent to each other in a circumferential direction of the cylinder, and the ejection of the fuel gas from the plurality of injection ports (132e, 232e) adjacent to each other is controlled by switching one switching valve provided at one of the branch flow paths.