OPPOSED-PISTON ENGINE

An opposed-piston engine includes: a cylinder; a one-side piston disposed inside the cylinder on one side in an axial direction; and an other-side piston disposed inside the cylinder on another side in the axial direction. Atop surface of the one-side piston has a one-side cavity recessed in a central portion. A top surface of the other-side piston has an other-side cavity recessed in a central portion. An outer peripheral edge of the one-side cavity is at least 0.1D1 away from an outer peripheral edge of the top surface of the one-side piston over the entire circumference, where D1 is a diameter of the top surface of the one-side piston. An outer peripheral edge of the other-side cavity is at least 0.1D2 away from an outer peripheral edge of the top surface of the other-side piston over the entire circumference, where D2 is a diameter of the top surface of the other-side piston.