To provide an apparatus for controlling a flow rate, which minimizes pressure losses.

The apparatus 1 for controlling the flow rate comprises a main flow channel and a flow route with fluctuation of one conductance or more and also uses a differential control valve with a pair of orifices, the conductance of the flow rate of which freely and differentially varies. A part of the differential control valve consists of a cylinder that includes a valve head 3, which has a first valve head unit located at one side of an axis direction of the cylinder and a second valve head unit located at the other side of the cylinder axis direction. Each of first orifice and second orifice is configured with the first and the second valve head units within a orifice body 2. The valve head 3 controls the flow rate by dividing the flow from the main flow channel, which is connected to a center unit of the valve head of the orifice body, into two flow routes by keeping a free position of the valve head to the direction of the axis.