To provide a gate valve such that two connected surfaces perpendicular to each other of a valve plate housing frame can be connected to two side walls perpendicular to each other of a chamber in such a manner that the connected surfaces are in contact with the side surfaces. When screwing a fixation screw perpendicularly into a screw hole formed in one chamber wall of a chamber through a screw insertion hole formed in one frame wall of a valve plate housing frame of a gate valve, and tightening the fixation screw to press and fix the frame wall against and to the first chamber wall, a thrust force in a direction perpendicular to the axis of the fixation screw is generated in the valve plate housing frame by a cam mechanism formed on the fixation screw and in the screw insertion hole, and the other frame wall of the valve plate housing frame is pressed against and fixed to the other chamber wall of the chamber by the thrust force.