A variable compression ratio internal combustion engine including: - a control shaft rotatably supported by an engine body, - a variable compression ratio mechanism for changing an engine compression ratio in accordance with a rotational position of the control shaft, - an actuator that is configured to rotatively drive the control shaft, - a speed reducing mechanism for reducing a rotational power of the actuator and for transmitting the speed-reduced power to the control shaft, the speed reducing mechanism having a rotation shaft rotatably supported in a housing fixed to the engine body and a lever that connects the rotation shaft and the control shaft, - a rotation sensor for detecting a rotational position of one shaft of the control shaft and the rotation shaft; and - a reference position learning means for carrying out compression ratio reference position learning operation, based on a detection signal from the rotation sensor, in a state where the other shaft of the control shaft and the rotation shaft has been mechanically regulated by either a first stopper face or a second stopper face characterized in - that the first stopper face is a high compression ratio side stopper face located in the engine body such that a part of the control shaft abuts on the high compression ratio side stopper face when the control shaft has been rotated to a position of maximum rotation on a high compression ratio side; - that the second stopper face is a low compression ratio side stopper face located in the housing such that a part of the rotation shaft abuts on the low compression ratio side stopper face when the rotation shaft has been rotated to a position of maximum rotation on a low compression ratio side; and - that a surface accuracy of the high compression ratio side stopper face is set higher than a surface accuracy of the low compression ratio side stopper face. - a control shaft rotatably supported by an engine body, - a variable compression ratio mechanism for changing an engine compression ratio in accordance with a rotational position of the control shaft, - an actuator that is configured to rotatively drive the control shaft, - a speed reducing mechanism for reducing a rotational power of the actuator and for transmitting the speed-reduced power to the control shaft, the speed reducing mechanism having a rotation shaft rotatably supported in a housing fixed to the engine body and a lever that connects the rotation shaft and the control shaft, - a rotation sensor for detecting a rotational position of one shaft of the control shaft and the rotation shaft; and - a reference position learning means for carrying out compression ratio reference position learning operation, based on a detection signal from the rotation sensor, in a state where the other shaft of the control shaft and the rotation shaft has been mechanically regulated by either a first stopper face or a second stopper face - that the first stopper face is a high compression ratio side stopper face located in the engine body such that a part of the control shaft abuts on the high compression ratio side stopper face when the control shaft has been rotated to a position of maximum rotation on a high compression ratio side; - that the second stopper face is a low compression ratio side stopper face located in the housing such that a part of the rotation shaft abuts on the low compression ratio side stopper face when the rotation shaft has been rotated to a position of maximum rotation on a low compression ratio side; and - that a surface accuracy of the high compression ratio side stopper face is set higher than a surface accuracy of the low compression ratio side stopper face.