PURPOSE: To extend upper limit of speed for the mechanism where a valve timing variable means is provided on either or both of suction or/and exhaust valves by altering the speed that is to be a standard to reduce the engine output during acceleration according to the alteration of valve timing.

CONSTITUTION: In a valve timing variable means, suction and exhaust valves are driven open/close by means of a cam for low speed in a non-connected condition of a driving rocker arm and a free rocker arm, as well as by means of a cam for high speed in a connected condition of these, and the connected condition is switch-controlled by means of controlling an electromagnetic valve 19 by an electronic control circuit 7 through a switching mechanism. In the electronic control circuit 7, when an engine driving is so accelerated that the engine speed reaches the predetermined high speed, a fuel injection valve 6 is controlled in such a way that the engine output is reduced. The speed that is to be a standard for judgement in reducing the engine output is altered according to the switching operation of valve timing.