Flow rate ratio control device, control program for a flow rate ratio control device and control method for a flow rate ratio control device

A flow rate ratio control device smoothly switches branches without generating abrupt changes in the flow rates of a fluid flowing therethrough. The device includes at least two branches from a main flow path, first and second fluid control valves each including a position sensor for a valve body, a storage unit that stores reference positions of the valve bodies in order to divide the fluid flowing into the branches at predetermined ratios, and a control unit that controls the ratios of the branches by performing position control to place the valve body of the first valve in the reference position, and by performing flow rate control to set the flow rate of the second valve to a target flow rate. When the valve body of the second valve reaches the reference position, the control unit switches the position control and flow rate control between the valves.