PURPOSE: To simplify a structure and obtain proper and efficient intake/exhaust function in high-speed operation of an engine by performing complicated function of valve mechanisms having conventional combination of a cam shaft and spring by a rotary shaft type intake valve and a rotary shaft type exhaust valve.

CONSTITUTION: A rotary shaft intake groove 3 and an intake port communicating groove 4 are formed on a rotary shaft 1 for intake valve, to obtain a rotary shaft type intake valve. This is the basic structure of an intake valve in every cylinder. A rotary shaft exhaust groove 5 and an exhaust port communicating groove 6 are formed on a rotary shaft 2 for exhaust valve, to obtain a rotary shaft type exhaust valve. This is the basic structure of an exhaust valve in every cylinder. These structures are prepared by required numbers corresponding to the cylinders. The intake sides and exhaust sides are arranged in pair in combustion chambers of heads of the cylinders.