Valve and shock absorber

A valve comprising:

• a valve seat member equipped with a port and a seat portion, the seat portion protruding from an end portion of the seat portion on an outlet end side of the port and surrounding the outlet end, and part of the seat portion including a plurality of circular arc shaped portions arranged on an identical circumference;
• a leaf valve having a circular annular shape, an inner periphery of the leaf valve being immovably laid on top of the valve seat member and an outer periphery of the leaf valve being to be spaced apart from or seated on the seat portion;
• and
• an annular plate stacked on a side of the leaf valve opposite to the valve seat member, wherein
• an outer diameter of the leaf valve is larger than a diameter of a virtual circle passing through an inner periphery on a seat surface of each of the circular arc shaped portions that the leaf valve to be spaced apart from or seated on, and is smaller than a diameter of a virtual circle passing through an outer periphery of the seat surface of each of the circular arc shaped portions,
• an outer diameter of the annular plate is set to be equal to or larger than a diameter of a virtual circle passing through an inner periphery on the seat surface of each of the circular arc shaped portions, and
• the leaf valve includes
• a cutout orifice having an opening from an outer periphery, and
• a protrusion protruding outward from one side or both sides in a circumferential direction of the cutout orifice on outer periphery.