To provide a variable valve opening characteristic internal combustion engine capable of improving the degree of freedom in setting valve opening characteristics while employing a comparatively simple structure.

A variable valve train includes, as main structure elements, an electric motor 21, a worm 23 attached to a shaft 21a of the electric motor 21, a worm wheel 23, a screw shaft 24 screwed in a female screw 23a formed in the axial center of the worm wheel 23, a slider 25 integrally formed at the lower end of the screw shaft 24, a control shaft 26 fitted in a horizontally long oblong hole 25a formed at the slider 25, a roller link 27 with the control shaft 26 fitted and inserted to the base end thereof, a roller 29 rotatably supported at the end of the roller link 27 through a roller shaft 28, and the like. An approximately L-shaped guide hole 39 with its intermediate part directed outward is formed at a cam holder 12, and the control shaft 26 is inserted into the guide hole 39.