PURPOSE: To provide such an engine structure as being capable of selecting operation at low fuel consumption or high power operation by driving a part of cylinders in the operation range of eight cycle driving, and driving the other cylinders in the operation range of 4 cycle driving and driving another part of the cylinders in Mirror cycle by using cam for driving the engine valves.

CONSTITUTION: An engine structure is provided with engine valves comprising an air intake valve 3 and an exhaust valve 4 and a plurality of cams 13 for driving the engine valves through a valve driving member 17, and one lifting operation of a part of cams 12 is made equivalent to one time rotation per 4 times rotations of a crank shaft, and the intake stroke and the exhaust stroke of the engine valve are made one times respectively. In the cam 13 of another part one lift operation thereof is made equivalent to one time per 2 times of rotation of the crank shaft and the intake stroke and the exhaust stroke of the engine valves. Are made one times respectively moreover, a timing for opening the engine valve is changed depeuling on the cams of one part and the cams of other parts.