An internal combustion engine including a variable compression ratio mechanism that changes a mechanical compression ratio, wherein the variable compression ratio mechanism includes: an operation element (54, 55); an input actuator that generates input torque to move the operation element; and a reverse input torque cutoff clutch that is disposed between an output shaft of the input actuator and the operation element in order to transmit the input torque from the input actuator to the operation element and to cut off reverse input torque from the operation element to the input actuator, and the variable compression ratio mechanism changes the mechanical compression ratio by moving the operation element, and the reverse input torque cutoff clutch includes: a fixed member; a movable member that is rotatable with respect to the fixed member; annular clearance that is defined by a peripheral surface of the fixed member and a peripheral surface of the movable member; a wedge member that is movably disposed in the clearance; and a moving device that moves the wedge member in the clearance, the output shaft of the input actuator and the operation element are connected to the movable member, the peripheral surface of the fixed member is formed such that the clearance is formed with: a rotation prevention area that prevents the movable member from rotating in the reverse input torque acting direction when the wedge member abuts against the fixed member and the movable member; and a rotation allowable area that allows the movable member to rotate in the reverse input torque acting direction; characterized in that the rotation prevention area is located on a downstream side of the rotation allowable area in the reverse input torque acting direction, and when the movable member moves in the reverse input torque acting direction to change the mechanical compression ratio, the moving device moves the wedge member from the rotation prevention area to the rotation allowable area in an opposite direction from the reverse input torque acting direction and holds the wedge member in the rotation allowable area, and the input actuator rotates the movable member in the reverse input torque acting direction, and in that the moving device has a moving member that includes an annular member and a rod member being attached to the annular member, wherein the rod member is provided corresponding to the wedge member and is disposed on the downstream side of the wedge member in the reverse input torque acting direction or is received by the wedge member in the clearance. an operation element (54, 55); an input actuator that generates input torque to move the operation element; and a reverse input torque cutoff clutch that is disposed between an output shaft of the input actuator and the operation element in order to transmit the input torque from the input actuator to the operation element and to cut off reverse input torque from the operation element to the input actuator, and a fixed member; a movable member that is rotatable with respect to the fixed member; annular clearance that is defined by a peripheral surface of the fixed member and a peripheral surface of the movable member; a wedge member that is movably disposed in the clearance; and a moving device that moves the wedge member in the clearance, a rotation prevention area that prevents the movable member from rotating in the reverse input torque acting direction when the wedge member abuts against the fixed member and the movable member; and a rotation allowable area that allows the movable member to rotate in the reverse input torque acting direction;