The invention provides a flow rate control valve capable of eliminating an extra operation of a diaphragm spacer after the valve is closed to thereby shorten a response time. A flow rate control valve comprises an annular valve seat (115), a diaphragm (116) having a fixed outer peripheral portion and produced from a thin plate-shaped elastic body, and a diaphragm spacer (117) located on the side opposite to the valve seat (115) with the diaphragm (116) interposed therebetween, the annular valve seat (115), the diaphragm (116), and the diaphragm spacer (117) being coaxially disposed. The flow rate control valve has a structure in which annular valve seat (115) has, at the top thereof, an inclined surface (123) inclined to the inner peripheral side, the diaphragm (116) is displaced toward the valve seat (115) by the pressing force of the diaphragm spacer (117), and thereby the inclined surface (123) at the top of the valve seat (115) and the diaphragm (116) come into contact with each other with no space therebetween.