To keep spring repulsion force as small as possible since micro entrance is slightly depressed when the micro entrance gripping a micro rotor provided at each corner of a rotor, a suction rotary valve, and an exhaust rotary valve touches and rotates, and unnatural force is applied on an intake rotary valve chord part, an exhaust rotary valve chord part, a rotor rear part and a rotor front part if spring repulsion force is large, although spring repulsion force need to be kept large since high pressure acts on the micro entrance 4 during explosion process.

This pressure cancellation hole is characterized by providing a hole passing to a section near the micro entrance 4 or to a spring chamber 1 at a bottom of the micro entrance 4 through the micro rotor and the micro entranced.