With respect to a minute flow rate controller comprising inflow passage (12) for introducing a fluid, valve member (2) furnished with main throttle groove (6) for causing the introduced flow to flow from a starting end toward a finishing end thereof, fluid outflow port (20) opened with an optional cross section by a flow rate regulating member and outflow passage (14) for leading out the fluid flowing out from the fluid outflow port (20), there is provided a method of designing the controller with entrance throttle groove, comprising providing the entrance throttle groove (8) communicably preceding the starting end position of the main throttle groove (6), and, on the basis of a relational expression derived from the momentum equation of the fluid flowing through the groove (8) and the main throttle groove (6), determining the size of the groove (8) so as to exhibit a desired flow resistance.