A uniflow scavenging 2-cycle engine (100) includes: a cylinder (110) in which a combustion chamber (140) is formed; a piston (112) sliding in the cylinder; scavenging ports (122) formed in an inner circumferential surface of one end of the cylinder in a stroke direction of the piston and suctioning an active gas into the combustion chamber according to the sliding motion of the piston; fuel injection valves (128) generating a premixed gas by injecting a fuel gas into the active gas suctioned from the scavenging ports into the combustion chamber; an exhaust port (116) formed in the other end of the cylinder in the stroke direction of the piston; exhaust valves (120) opening and closing the exhaust port; and an exhaust valve driving mechanism (118) opening and closing the exhaust valve such that a time required to displace the exhaust valve from a fully opened position to a fully closed position is longer than that required to displace the exhaust valve from the fully closed position to the fully opened position. With this constitution, an injection start timing of the fuel gas can be advanced while blow-by of the fuel gas is suppressed.