Abstract: In an opposed-piston mechanism, an intake compression cylinder and an expansion exhaust cylinder are individually provided, and a rotating perforated columnar valve and an ignition combustion chamber are formed therebetween. A valve mechanism is arranged on a cylinder side surface side, and a disk cam that moves in conjunction with crank rotation operates an intake valve and an exhaust valve on a cylinder side surface via a movable fulcrum type rocker arm. A movable structure of the rocker arm also realizes opening/closing amounts of the intake valve and the exhaust valve according to an operating situation of an engine. Since a piston pin and a piston pin can absorb variations of an engine that occur when two connecting rods are connected to one piston, the two connecting rods can be easily connected to the one piston.