According to an aspect, a gas supply mechanism for supplying a gas to a semiconductor manufacturing apparatus is provided. The gas supply mechanism includes a pipe connecting a gas source and the semiconductor manufacturing apparatus to each other, and a valve which is provided on the pipe. The valve includes a plate rotatable about an axis, the axis extending in a plate thickness direction, and a housing provided along the plate without contacting the plate to accommodate the plate, the housing providing a gas supply path along with the pipe. A through hole is formed in the plate, the through hole penetrating the plate at a position on a circle which extends around the axis and intersects the gas supply path.