An internal combustion engine includes a variable valve system wherein each cam opens and closes an intake valve and an exhaust valve via each rocker arm. A variable valve system of an internal combustion engine E includes rocker arms rocked by the action of valve driving force of cams with each lift quantity variable mechanism varying a maximum lift quantity of an intake valve and an exhaust valve. The lift quantity variable mechanism includes a lifter that is driven by the cam, and makes the valve driving force act on the rocker arm and a lifter holder that supports the lifter, and is driven by an electric motor and is rocked. The lifter is movably supported by the lifter holder. Maximum lift quantity is varied by varying a position in which the lifter abuts on the rocker arm according to a position in which the lifter holder is turned.