A flow rate control valve includes a casing provided with an inlet port and an outlet port through which a fluid, the flow rate of which should be controlled, flows in and out, a diaphragm that partitions a space inside the casing into a flow space in which the fluid flows and a working space in which a working medium is present, and a valve body provided on a portion of the diaphragm that opposes the inlet port. The diaphragm is displaced in accordance with a change in the internal pressure of the working space, and the valve body is accordingly moved. This results in a change in the distance between the valve body and the inlet port, and thus the flow rate of the fluid flowing into the flow space through the inlet port is adjusted. Therefore, the flow rate of the fluid flowing out through the outlet port is variably controlled.