PURPOSE: To provide a pure rotary shaft valve which can replace a conventional general reciprocating, oscillating dynamic valve mechanism, has a better heat dissipation as compared with the conventional valve and can minimize heat loss of an internal combustion engine by reduced slide parts and slide speed.

CONSTITUTION: A valve comprises a shaft member 2 having a through hole 22 running from side to side in a plane perpendicular to a longitudinal axis, and a jacket member 1 having an opening 20 corresponding to the through hole 22. The through hole 22 becomes in communication with an intake duct or a discharge duct twice via the opening 20 on the jacket member 1 to intake or discharge during one rotation of the shaft member 2. As a result, one rotation of the shaft valve corresponds to four rotations of an engine shaft or two rotations of a camshaft in a conventional dynamic valve mechanism.